So last Monday I ran my D&D group through a trap dungeon that I had a lot of fun making and got to thinking, to all the other GM's out there, what are some of your favorite traps?  To the players, what are some of the most fun traps you've come against?

There are the ones that were in my game last Monday:

• The Deep Door -- Every door was actually about two feet thick and had the lock drilled into about 2 feet so the players couldn't use lock picks.  The hole was just big enough for a human arm so it made it difficult for them to stick things in the hole too.  Most of the doors used only keys but one of the doors was just a handle they had to twist which made spikes dig into their arms.  This wasn't so much a super devious trap as more fun watching the group decide who would stick their arm in there.
• Rings of Pandora -- Stole this from God of War, I pretty much recreated the rings where they had to rotate the walls to position a lighting mechanism.  Each ring had a single use mechanism with 3 red, blue, and green lenses.  The hour doors on the outside each had a colored jewel that had to have that lights color shined on it.  Blue, yellow, and purple were easy for the group, they had to think for a while with orange.
• Countdown Trap -- The group comes to a long room with a button and a timer that reads 15 on it.  When the group reaches the middle of the room the traps arms itself and the door shuts.  When a player hits the button sand starts pouring in from the top and the timer starts counting down.  Every time they press the button again the timer resets.  The trap is disarmed by letting the timer reach 0.
• Greedy Room -- The players find themselves in a room full or brightly colored potions, a rack, and an electric chair with a small poem about greed.  The first potion or device they use is immensly beneficial while every one after that is horribly detrimental.  The key was in plain site behind some potions, the point of that one was someone randomly trying a potion and then getting others to try them as well after they results so turn out so good after the first.
• In and Out Box Puzzle -- Simple overused puzzle where you put something in a box you get someone similar value back.  The twist was that if you put in a common item you get a cursed item back.  The group first put in a normal staff and thought they got a staff of healing (forget the name, augmented the clerics healing) and then a coin purse and thought they got a magic coin purse back.  The rogue stuck his hand in the coin purse and it started eating his arm.  The only way to get it off was to bash it which also hurt the rogue.  The rogue was in pretty bad shape from the purse eating his arm and the party bashing him so the cleric tried to heal while holding the cursed staff which actually hurt him for how much she would normally heal him.  It was glorious.
• Spinning Platforms Puzzle -- This was another one inspired by God of War.  You have two circular platforms about 30 feet apart each with a plank that extends 10 feet.  The planks point away from each and allow you to walk onto the platform or off the platform.  The platform closest to the entrance of the room has a button that quickly spins the two platforms around so the two planks line up for a moment so there's only a 10 foot gap between the two platforms.  Below the platform is a spiked pit and handholds going up the wall.  Most players should miss that there are poisoned spikes in the handholds on the wall.  Getting to the other side of the room isn't too hard, a simple acrobatics check gets you to the other side but getting back is the problem since you don't have access to the button.  If a player falls into the pit (and they will) they'll take falling damage and then more damage from the spiked floor.  When they try to climb out of the pit, they'll likely miss the poisoned hand holds and poison themselves.  That was my favorite trap of the night.

And another fun trap I had in an old campaign.

The players were in a region that was more or less Antartica and were in a crazy old wizards tower (aren't they always just that?). The wizard being crazy decided to have his castle built out of ice and then have alchemist fire flowing through the walls.

Now what do you think the curious adventurer does when they see a castle made completely out of ice with a bunch of liquid flowing through the walls? Do you think they might pound on that wall to see what the liquid is?

Only if they have 8 Wisdom.

Of course, 8 Wisdom is one of the absolute greatest stat scores to have because it allows you to do tons of mind-bogglingly stupid and hilarious things while still remaining more or less "in character."