> Even a 4D maze; let's call it a 3D maze with time-travelling. Could be just 3 "squares" deep in the 4th dimension for a start: "yesterday", "today" and "tomorrow".

Have you seen this?

"Miegakure [Hide & Reveal] is a game where you navigate a four-dimensional world to perform miraculous feats and solve puzzles."

http://miegakure.com/

Mind-boggling is a good word for it!