https://www.youtube.com/watch?v=cuRhaRJUtWw#t=463
Duke Lives
1. Admire the hot Duke himself in the mirror in the bathroom of Duke's apartment.
2. Take a leak in the same bathroom of Duke's apartment.
3. Sink all balls in pool in Duke's apartment.

Damn! It's Late
4. Pop some popcorn. After exiting the elevator and going down the stairs there will be 3 guys watching the news. Go into the room to the left.
5. Sign the boy's autograph

The Duke Cave
5. Bench press 600 pounds in Duke's gym. You have to add the weights yourself. There are three on the floor and one on a bench in the bottom right corner of the room.
6. Curl a dumbbell in Duke's gym.
7. Punch the punching bag in Duke's gym.
8. Punch the speed bag in Duke's gym.
9. Score with a basketball in Dukes' gym.
10. Play pinball and get a score of 280.000 in Duke's gym.

The Lady Killer
11. Win at the slot machine.

Vegas in Ruin
BOSS BATTLE

The Duke Dome
12. Copy Duke's butt in the copier found in the construction office. That's the building you find to your right after you have walked through a container you blow down.

The Hive
13. Slap some breasts on the wall.

Duke Nukem's Titty City
14. Try out the glory hole in the strip club toilet.
15. Request a special dance by the stripper on the strip table in the main room of the strip club.
16. Watch at dirty DVD in the strip club office. The office is located behind the bar, use code 4768 to get in. Once in there, the DVD is placed on the desk. Take it to the DVD player and put in the DVD.
17. Win a game of poker in the Game Room.
18. Win a game of Alien Abortion in the Game Room.
19. Win a game of air hockey in the Game Room.

Crash Course
20. Throw a frisbee - After wandering around on some tentacles you'll have to smash through some alien eggs and jump down to a lower level. To the right on the walkway you land on you'll find two frisbees lying on the ground.

The Duke Burger
21. Smoke a cigar. As soon as the Chapter begins, turn around and continue down the hallway. You will soon come to an end of the hallway, and there you'll find a red door to the left. Enter the door to the next room and look on a shelf in the back of the room.
22. Read a dirty magazine. You'll come to a toilet in which you have to shrink yourself in order to proceed. Open the first toilet door and look on the floor.

The Mighty Foot
23. Watch the babes sunbathing on a pier using binoculars - After your monster truck runs out of gas for the first time, and you have gone to find some more gas, you'll come to a spot where there's a small building to the right of the highway. Ignore that building and look on the left side of the highway. There will be two binoculars with some benches around them.
24. Look at some naughty pictures on the PC found in the building stated above.

Ghost Town
25. Read another dirty magazine. After the monster truck runs out of gas once again, look to the right and you'll see a building, possible a church. Enter it and look under one of the benches to the right.

Dam Top
26. Have fun with a paper plane. After the boss fight with Battlelord on the highway, go all the way to the end of the highway and you'll see a yellow school bus. Take a look inside the bus.

The Shrunk Machine
27. Look in the calendar. After you have got the Freeze Gun and entered the room with a lot of aliens, you'll see a double door. Enter that room and turn around. It's hanging on the wall to your right.

The Forkstop
28. Read one more dirty magazine. In the beginning of the Chapter you will have to turn on the power to be able to raise up the garage door. In the same room as you turn on the power, look on the shelf behind the door you opened to get in there.

https://www.youtube.com/watch?v=zkRTwrS0OZ8
Rude Awakening = 1
After leaving the torture room, use the toilet that you see in the next room.

Going Down = 1
After killing the 1st patch of enemies, you'll enter a room with a dead scientist. Look at the porno magazine on the desk.

In Security = 2
After jumping out of the vents, examine the computer for porno.
After searching for porno on the computer, turn around and drink the bottle of beer.

The Clone Carousel - 1
After the Terminator battle in the room with the mounted turret; continue on into the next room and climb up both the staircase to examine the porno magazine on the desk.

Me, Myself, and I = 9
In Skill Training room; shoot the basketball into the hop. I suggest standing in front of it for better results.
In Melee Training room; punch the punching bag
In Melee Training room; admire yourself in the mirror.
In Melee Training room; use the pull up bar after admiring yourself in the mirror.
In Melee Training room; go over to the Duke clone and win/break his arm in an arm wrestling match.
In Weight Training room; curl a dumbbell weight.
In Weight Training room; lift the weights in front of the mirror.
In Weight Training room; place all 6 weights onto the empty bench press, then lift it up.
Story related; use the glowing switch and grab the film reel and insert it into reel the projector.

The Doctor Is In = 1
Story related; defeat the boss.

Magic Carpet Ride - 1
After making it past the enemies and using the ladder to climb out of the elevator. You'll find a glowing switch, flip the switch and turn around and enter the door behind you. Kill the two Pig Cops aliens and go down the walkway and turn left to find a dart board. Grab a dart and step back and throw the dart onto the dart board.

The Burning Bush = 5
Earn a 250,000 pinball score on the Scientits pinball machine
Complete the Duke Nukem machine (more like Space Invaders). There's only three levels and defeat the Boss
Use toilet upstairs in the second room on the right.
On the right side of the main room near the bar there is a dart board on the wall.

Duke Side of the Moon = 1
After your moon rover is broken down and you have to remove its power cell, search the ground nearby it for the American flag. It's the moon rover that has the EDF ammo crate right next to the moon rover.

Quake 2 engine, 1996-1998:
Duke Nukem Forever was officially announced on April 28, 1997, with the intention of releasing the game no later than mid-1998. Barely a year after the release of Duke Nukem 3D, the game's graphics and its game engine, the Build engine, were antiquated. Id Software's new Quake II engine was far superior to Build, so Broussard decided to license it. The price spent for the licensing rights was steep estimates were as high as $500,000 but Broussard reasoned that it would save time used to write a game engine from scratch. Broussard and Miller were flush with cash from the sales of Duke Nukem 3D and other games, so they decided to fund Duke Nukem Forever themselves, turning marketing and publishing rights over to GT Interactive.

In August and September, the first screenshots of Duke Nukem Forever were released in PC Gamer. However, 3D Realms did not receive the Quake 2 engine code until November 1997, and the earlier screenshots were mock-ups with the Quake engine that the team had made in their spare time. 3D Realms unveiled the first video footage of Duke Nukem Forever using the Quake II engine at the 1998 Electronic Entertainment Expo (E3) conference. The trailer showed Duke fighting on the back of a moving truck and firefights with aliens. While critics were impressed, Broussard was not happy with the progress being made.

Unreal engine, 1998-2003:
Soon after the release of the Quake II engine, Epic MegaGames had unveiled its own Unreal Engine. The Unreal Engine was more realistic than Quake 2 and was better suited to producing open spaces. 3D Realms had been struggling to render the Nevada desert. Soon after E3, a programmer suggested that they make the switch. After discussions, the developers unanimously agreed to the change, which would mean scrapping much of their work so far, including significant changes 3D Realms had made to the Quake Engine. In June 1998, 14 months after the Quake 2 announcement, 3D Realms made the switch announcement. Broussard said that the game would not be "significantly delayed" by the switch, but that the project would be back to where it was at E3 "within a month to six weeks". Broussard also said that no content seen in the E3 trailer would be lost. Chris Hargrove, one of the game's programmers at the time, confided that the change amounted to a complete reboot of the project.

By the end of 1999, Duke Nukem Forever had missed several release dates and was largely unfinished; half the game's weapons remained concepts.[11] Broussard shot back at criticisms of the game's lengthy development time as the price paid for developing complex modern games: A significant factor contributing to the game's protracted development was that Broussard was continually looking to add new elements to the game. A running joke at 3D Realms was to stop Broussard from seeing a new video game, as he would want to include portions of it in Duke Nukem Forever. Later that year, Broussard decided to upgrade to a new version of the Unreal engine that was designed for multiplayer matches. Former employees recalled that Broussard did not have a plan for what the finished game would look like.[11] At the same time, GT Interactive was facing higher-than-expected losses and hired Bear Stearns to look into selling the company or merging it.[16] Later that year, Infogrames Entertainment announced it was purchasing a controlling interest in GT Interactive.[17] The publishing rights for Duke Nukem Forever passed to Gathering of Developers in early December 2000.[18]

To placate anxious fans, Broussard decided to create another trailer for E3 2001, it was the first public look at the game in three years. The video showed a couple of minutes of in-game footage, which notably showed the player moving in what appears to be Las Vegas and a certain level of interactivity (the player buys a sandwich from a vending machine and pushes each individual button on a keypad with Duke's outstretched finger). The trailer was impressive, and Duke Nukem was the talk of the convention; IGN reported on the game's graphics, saying, "Characters come to life with picturesque facial animations that are synced perfectly with speech, hair that swings as they bob their heads, eyes that follow gazes, and more. The particle effects system, meanwhile, boasts impressive explosion effects with shimmering fire, shattered glass, and blood spilt in every direction Add in real-time lighting effects, interactive environments, and a variation in locales unequaled in any other first-person shooter and you begin to see and understand why Duke Nukem Forever has been one of the most hotly anticipated titles over the last couple of years." Duke Nukem Forever looked as good or better than most games, and staff at 3D Realms recalled a sense of elation after the presentation; "The video was just being eaten up by people," one said. "We were so far ahead of other people at the time." While many of the staff expected Broussard to make a push for finishing the game, however, he still did not have a finished product in mind.[12] Following the death of one of Gathering of Developers' co-founders and continuing financial problems, the publishers' Texas-based offices were shut down and absorbed into parent company Take-Two Interactive.

Conflict with Take-Two, 2003-2006:
By 2003, only 18 people at 3D Realms were working on the game. One former employee said that Broussard and Miller were still operating on a "1995 mentality", before games became large-team, big budget development affairs. Because they were financing the project themselves, the developers could also ignore pressure from their publisher; their standard reply to when Duke Nukem Forever would ship was "when it's done". In 2003, Take-Two CEO Jeffrey Lapin reported that the game would not be out that year. He further said the company was writing off $5.5 million from its earnings due to Duke Nukem Forever‍ '​s lengthy development time. Broussard shot back that "Take-Two needs to STFU ... We don’t want Take-Two saying stupid-ass things in public for the sole purposes of helping their stock. It's our time and our money we are spending on the game. So either we're absolutely stupid and clueless, or we believe in what we are working on." Later that year, Lapin said 3D Realms had told him that Duke Nukem Forever was expected to be finished by the end of 2004, or the beginning of 2005.

In 2004, video game website GameSpot reported that Duke Nukem Forever had switched to the Doom 3 engine. Many gaming news sites mailed Broussard, asking him to confirm or deny the rumor. After receiving no answer from him, they published the rumor as fact, but Broussard explicitly denied the rumor soon after. Soon after 3D Realms replaced the game's Karma physics system with one designed by Meqon, a relatively unknown Swedish firm. Closed-doors demonstrations of the technology suggested that the physics of Duke Nukem Forever would be a step up from the critically acclaimed Half-Life 2. Rumors suggested that the game would appear at 2005 E3. While 3D Realms' previously canceled Prey made an appearance, the rumors of Duke Nukem Forever‍ '​s appearance proved false.

Broussard reported in a January 2006 interview that many of Duke Nukem Forever‍ '​s elements had been finished; "we're just basically pulling it all together and trying to make it fun". Later that year Broussard demonstrated samples of the game, including an early level, a vehicle sequence, and a few test rooms. Among the features seen was the interactive use of an in-game computer to send actual e-mails. The developer seemed contrite and affected by the long delays; while a journalist demoed the game Broussard referenced note cards and constantly apologized for the state of the game. In filing with the United States Securities and Exchange Commission, Take-Two revealed they had renegotiated the Duke Nukem Forever deal, with the former publisher receiving $4.25 million instead of $6 million on release of the game. Take-Two offered a $500,000 bonus if Duke Nukem Forever was commercially released by December 31, 2006. However, Broussard denied the rumors that DNF would be released, saying that 3D Realms never cared for or asked for the bonus. He stated that he would "never ship a game early."

Some of the staff were tired of the delays. Duke Nukem Forever was the only 3D game many had worked on, giving them little to put on a resume, and as much of 3D Realms' payment hinged on profit-sharing after release, the continual delays meant deferred income. By August 2006, between 7-10 employees had left since 2005, a majority of the Duke Nukem Forever team (which in recent months had shrunk to around 18 staff). While Shacknews speculated that the departures would lead to further delays, 3D Realms denied the claims, stating that the employees had left over a number of months and that the game was still moving ahead. Creative director Raphael van Lierop, hired in 2007, played through the completed content and realized that there was more finished than he expected. Lierop told Broussard that he felt they could push the game and "blow everyone out of the water", but Broussard responded that the game was still two years away from completion.

3D Realms final years in development, 2007-2009:
The long delay strained Broussard and Miller's relationship, and by the end of 2006, Broussard appeared to become serious about shipping the title. On January 25 and May 22, 2007, Broussard posted two Gamasutra job ads with small screenshots of Duke Nukem and an enemy, which he later confirmed were real in-game screenshots. The team doubled in size within a short timeframe. Among the new hires was project lead Brian Hook, who became the first person to successfully resist Broussard's requests for changes.

A new game trailer was released on December 19, 2007, the first teaser in more than six years. The video was made by 3D Realms employees as part of holiday festivities. While Broussard maintained the release date would be "when it's done", he added that "you can expect more frequent media releases and we have considerable work behind us". While the Dallas Business Journal "confirmed" a 2008 release date for the game, Broussard later reported that this was based on a misunderstanding of "off the record" information. In-game footage of the game appeared in 2008 premiere episode of The Jace Hall Show. Filmed entirely on hand-held cameras but not originally expected to be publicly released, the video showed host Jason Hall playing through parts of a single level on a PC at 3D Realms' offices. The footage was confirmed to have been shot six months prior to the episode air date and according to Broussard, contained outdated particle and combat effects that had since been replaced. The game did not make an appearance at E3 2008, an event which Miller described as "irrelevant".

While the game neared completion, the funding began to dry up. Having spent more than $20 million of their own money, Broussard and Miller asked Take-Two for $6 million to complete the game. According to Broussard and Miller, Take-Two initially agreed, but then only offered $2.5 million. Take-Two maintained that they offered $2.5 million up front and another $2.5 million on completion. Broussard rejected the counteroffer, and on May 6, 2009, suspended all development.

DNF team laid off and 3D Realms downsized, 2009-2010:
3D Realms laid off the DNF staff on May 8, 2009 due to lack of funding, but inside sources claimed it would still operate as a smaller company. Development on DNF halted, and its fate was unknown. Publisher Take-Two Interactive, in response, stated that they still held the publishing rights for Duke Nukem Forever, but they were not funding the game. Prior to and after the action, unreleased screenshots, concept art, pictures of models from the game and a goodbye message from 3D Realms were posted by alleged former employees. Similar leaks followed after May 8, 2009.

Take-Two filed a lawsuit against 3D Realms over their failure to complete Duke Nukem Forever, citing that they paid $12 million to Infogrames in 2000 to acquire the publishing rights. 3D Realms argued, however, that they never received that money, as it was a direct agreement between Infogrames and Take-Two. The lawsuit seemed to be over a contractual breach, but not regarding the $12 million mentioned above. Take-Two asked for a restraining order and a preliminary injunction, to make 3D Realms keep the Duke Nukem Forever assets intact during proceedings, but the court denied the publisher's request for a temporary restraining order. In December 2009, Apogee CEO Scott Miller clarified that "we've never said that Duke Nukem Forever has ceased development, though we released the internal team, but that doesn't correlate to the demise of the project."

3D Realms made plans to hire an "external" developer to complete the progress while continuing to downsize itself, resulting in development on another title known as Duke Begins being halted. An unofficial compilation of gameplay footage was also released in December 2009. By 2010, 3D Realms and Take-Two had settled the lawsuit and dismissed it with prejudice.

Gearbox revival and release, 2010-2011:
Despite the discontinuation of internal game development at 3D Realms, development of the game did not cease entirely. Nine ex-employees including key personnel like Allen Blum, continued game development throughout 2009 from their homes. These employees would later become Triptych Games, an independent studio housed in the same building as Gearbox, with whom they collaborated on the project.

After ceasing internal game development, 3D Realms approached noted game developers Gearbox Software and asked them if they were interested in helping Triptych Games polish the nearly finished PC version and port it to the consoles. Gearbox CEO Randy Pitchford, who had worked on an expansion to Duke Nukem 3D and very briefly on Forever before he left to found Gearbox, felt that "Duke can't die" and decided that he was going to help "in Duke’s time of need." He started providing funding for the game and contacted 2K Games' president to persuade his company that Gearbox and Triptych can complete the development of the game and get it released on all platforms in time. Duke Nukem Forever was originally intended to be a PC exclusive game, however 2K and Gearbox had hired Piranha Games to port the game designed for PC to Xbox 360 and PlayStation 3 and added a Multiplayer in order to raise sales.

The game was officially re-announced at the Penny Arcade Expo 2010 on September 3, 2010. It was the first time in the game's development history that gamers were able to actually try the game, according to Pitchford, "the line has gotten up to four hours long to see the game". Gearbox Software subsequently purchased the Duke Nukem intellectual property from 3D Realms, and 2K Games held the exclusive long-term publishing rights of the game.

Development was almost complete with only minor polishing to be done before the game was to be released in 2011. A playable demo of Duke Nukem Forever was released once Gearbox figured out the timing, with purchasers of the Game of the Year Edition of Borderlands gaining early access. The demo is unexpectedly different from the versions available at PAX and Firstlook. Those that purchased Borderlands on Valve's Steam prior to October 12, 2010 got the code for the demo without the need to buy the Game of the Year edition of the game. Duke Nukem Forever was initially scheduled for release on May 3 in the United States and May 6 internationally and after another delay was finally released on June 14 in North America and June 10 worldwide, nearly four weeks after the game had gone gold within 15 years.

By completing the game on any difficulty, you will get to unlock extra options for your next playthough. Most of these can be Unlocked on Normal Mode or Higher. (The options labeled "CHEAT" will disable achievements and Ego points.)

Duke 3D Freeze Ray = Freeze ray will fire bouncing ice projectiles (SP only).
Game Speed = Adjust game speed (SP only).
Grayscale Mode = Draw the game in grayscale (SP only).
Head Scale = Adjust head size of enemies and NPCs (SP only).
Infinite Ammo = Never run out of ammo (SP only). CHEAT.
Instagib = Enemies die in 1 shot and always gib (SP only). CHEAT.
Invincibility = Take no damage from bullets or explosions (SP only). CHEAT.
Mirror Mode = Draw the game mirrored horizontally (SP only)

Key Codes:
Doctor Who Cloned Me, Rude Awkening = 1503 (Small Hallway which leads to the Elevator)
Duke Nukem Forever, Duke Nukem's Titty City = 4768 (Manager's Office in the Main Show Room)