https://www.pcgamer.com/the-witness-is-free-on-the-epic-games-store/

The Witness, the lovely but baffling 2016 puzzle game from Braid creator Jonathan Blow, is now free on the Epic Games Store. Click here, click "free," and just like that, it's yours for keepsies. 

I'll be honest, I didn't like The Witness as much as I wanted to. It's a stunning game and wonderfully atmospheric, but the puzzles get really dense, and I just don't have the patience (or, I suppose, the brain) to get my head around the later-game stuff. Taking a break just made it worse: When I came back a few weeks later I'd completely forgotten most of what I'd learned, and so had to replay much of the early game to get re-acquainted with it. By the time I hit the tough stuff again, I was done with it—again—and accepted that whatever mysteries it holds will be hidden from my eyes forever.