A Magical Puzzle Key for opening a door. Innocuous, somewhat simple, but fun to solve, if you like puzzles.
A magical barrier of acid blocks your path. Solve the puzzle to unlock the door.
A combination lock, possibly to open a chest or door or other entry point. A magical puzzle, for those interested.
Checkerboards on floors of dungeons… is there any greater bane to adventurers?
The multiple-worlds theory of cosmology allows room for every religion's Heaven and Hell and other planes to coexist, with the similar planes of all the sapient beings of all the worlds in all the galaxies...How often do the wires get crossed, as it were, leaving your paladin in a Hell for hedonistic lizards, for example.