What is point of no return in The witness?

I'm feeling like i'm very close to an ending of The Witness, even though there are a lot of puzzles are left unsolved. And I heard that it is possible to beat the game without solving all the puzzles.

Can someone formulate a recognizable description of the action, which forbid me to go back and solve rest of the puzzles? With minimum amount of spoilers, please.

Solution 1:

There is not really a point of no return you need to worry about. While there is a point that triggers the ending which you then can't abort, you'll be able to recover the savegame and complete the other puzzles (and I believe this is how the game is intended to be played).

When you do complete the game it will quit (on PC at least) and when you restart it, you'll start from a fresh savegame, but you can then enter the menu and load your previous savegame. That last (auto-)save will always be just before the actual point of no return. The OP said the game loaded that savegame automatically upon restarting the game, so maybe this was changed in a recent update. (Also, I vaguely remember from some YouTube video that the PS4 version will just present you with the loading menu right away instead of quitting the game.)

If you really want to know the "point of no return" that requires you to load the last save:

There's an elevator in the water, that is activated via two simple "puzzles" (they're just straight lines, I think). When you activate the elevator, then the ending sequence starts.

Some spoilers here, you might not want to read them until you've solved a lot more puzzles:

The same thing is true for the alternative ending. The "point of no return" here is actually a few minutes of gameplay worth before the actual end of the game, but when you load the savegame you'll still start from before that point. The next spoiler block contains that point.

When you solve the "hidden (environmental) puzzle" that involves the sun and the structure around the gate of light in the starting area, you open up the final area that leads to the alternative ending. This can't be undone, and you cannot leave the starting area once you do, unless you load that savegame.

Solution 2:

There's no point of "no return" at any point in the game. You can do anything at any point and come back to continue after doing anything else.

There are a few things to note:

• Many "one way" mechanics like moving platforms and elevators will automatically come to your place when necessary, for example,

  two yellow platforms in the swamps, the elevator between the middle layer and the bottom layer inside the mountain, the quarry elevator

• If you complete the game in the canonical way, it will send you back to where you started, with a fresh save data (PC, unsure for console/iOS). However, right before the last action of completing the game, your data is saved, so you can immediately load that save and quit the "end area" and continue your exploration.

• There is a huge secret in the game, which

  Replaces a gate with a completely new area, usually referred to "the alternate ending".

  Although it's sometimes considered a "no return" point, actually

  If you pause the game and load any other save data, or if you just close the game and start it again, you'll see yourself standing right before that "alternate ending" area, without having it activated.

  In other words, this "no return" point

  does not preserve across game sessions