@dis0nored I don't know if you already beat the puzzle since your comment is almost 4 years old, but here it goes:

In the underground maze, there's a dead body in that big "Main Chamber" room with a note containing the 1st and last symbol for the gate. You're supposed to run around the maze searching for 4 more dead bodies with 4 more notes for the 4 other settings for the lock.

In practice, if you don't want to bother with that jumpscare-heavy section, you can just run straight to the Main Chamber (only going another way temporarily if the Cursed Miner spawns in front of you) and use a screenshot from a guide to enter the 6 symbols on the gate, triggering the relevant cutscene(s).

What are you suppose to do in the mines? I'm at the cave with lots of hallways and candles everywhere. I walk around for a bit, a dead guy with lantern shows up and gets you. Tho After a few times he lays there dead again, you inspect it and end up at the top of a cliff with a gate. haven't got a clue what to do with the gate because

There isnt first screenshot.

I picked up the grenade before doing the train, when I found the arched part of the dam the words floated "Throw grenade". When they settled I LMB clicked and the grenade went off. At the lower dam after turning the turbine off I found the shallow rocky shoreline and there was the diver and his rifle. Was no issues at all for me just didn't have a clue what it all meant was all.

Anyone having an issue where the dead body (diver guy) isn't showing up? Restarted the game 3 times and still having the same problem (can't pick up the gun because he's not there) :/

I had the same problem, and I've spent quite a few minutes to throw it too, so I know it can be done :D

But what do you know, running around the same spot for 5 minutes and randomly clicking did actually throw it. You're right!

I do get the floating "throw grenade" text, if that's what you mean, but there's no action available.

You CAN throw it, it's just very hard to fish for the trigger pixel, especially if you don't know where it is supposed to be.

Yeah, as mentioned in the original game's thread, don't pick up the grenade too early. I did before completing the space thing, and now I can't throw it. Obviously the grenade wasn't at the pickup location either. -> Restart game