Ending 4: Lost
Pick up the Craftman's key from the table. You should have two mysterious artifacts in your possession after running through the release endingand the escape ending. With these three things in your inventory - and the screwdriver - head through the portal.
Put the Craftman's key onto this mechanism to open it.
Take the metal ring from the edge of the table.
Use the metal ring on the box and use the eyepiece to look inside.
Line up the holes again as we did with the other endings so that they're underneath the pistons.
Move the mirror over to the left to divert the beam and grab the second mirror from the usual compartment under the table.
Pop it onto the inner ring and return the first mirror to its original position.
Use the eyepiece to look inside the Craftman's key and solve the laser puzzle.
Ignore the train door. Place the artifacts on the podiums. Look at the rear of the one on the right and use the screwdriver on the metal plate.
Pull the plate back to reveal a lens, then turn the dial on the front and use the eyepiece to look inside.
Figure out the laser problem once more, zoom out of the box and press the button on the top. Ignore the wooden door and head over to theotherartifact.
Use the eyepiece to look inside and solve this puzzle again. Zoom out and press the button on the top.
There should be three projector lights shining on the screen, and instead of a door you'll just see a hole. Step through for last ending.
And that's it. You've solved all of the needlessly elaborate puzzles apart from the one that really matters: What is the Null and what's at the end of all of those tentacles?