Mirrors is another prototype concept where the player can walk through mirrors into a revers world. The system I've developed allows for seamless walking through mirrors into reverse world, upside-down world, as well as 45 degree angle world (walking on walls). Since gravity needs to be flipped and rotate, the Unity physics engine could not be used. It also allows for items to exist in the real or reversed world and seen in the reflection. Water, as in the picture above, or any reflection can be jumped into with the same result as going through a mirror.
I have not decided the forum to explore the concept, I started with the sci-fi prototype below (ignore the frame rate, that was a recording glitch). I updated to an Escher like world above but am still considering a murder mystery: Murder Mansion and the Mirror Maze. In that concept ghosts would inhabit the mirrors and could potentially be able to interact with you in either side of the mirror. It could also have a puzzle solving spin where a given mirror would send you back in time to when the murder took place.