30 Days of D&D Day 13: Favorite Trap/Puzzle

Let's see, my favorite trap or puzzle. Though my favorite play location is in fact ruins, and that seems like the most likely place to find traps and puzzles, I had to rack my brain a bit for this one.

And really, it's an odd question, because I find traps to more of a "I hope this doesn't kill me/us" far more than "ooh, a puzzle!"