Not a shooter, but superliminal I think has a few levels that let you use portals to change your size, and there’s no limits on how many times you can do it, so you can shrink yourself to be microscopic to the point where you can fit inside a straw and it takes like a minute to walk to the end of the straw. Everything in the room is modeled to be quite detailed, so there’s also a chess board, and you can get on top of the rook piece and it’s like being on top of a castle.

Pretty fun puzzle game