Another trap of the "you're going to trigger this purposely to get the loot" variety. Treasure-hungry adventurers should figure out a way to get this down. It's not very dangerous, unless the players do something insane - and they usually do. As I've mentioned in other posts, I like this style of trap - make it obvious, but make the bait compelling.
114. Golden Pendulum
In the center of this room is a 3’ square wooden platform, six inches high, supported by a series of dowels. The wood is incredibly old and fragile, and it will break easily if disturbed. Carved into the top of the platform are the words “Warning: Pressure plate beneath. Do not disturb.”
There is indeed a pressure plate beneath the platform, easily spotted now that players know to look for it. Moving the platform will cause it to start snapping – players will need to take care to prevent it from triggering the trap.
Any pressure on the plate will cause a blade at the end of a long bronze chain to swing down from the ceiling, causing 3d6 points of damage (save vs. petrification for half damage) to anyone standing in its path (running from southeast to northwest through the center of the room). The blade has a second chain connected to it, running from the southeast end of the slot, that will immediately start pulling the chain and blade back into the slot after the trap has swung once.
The blade is cast from solid gold, and is worth 400 gp. Close inspection will reveal the blade’s edge is a thin length of razor-sharp carbide steel embedded into the gold body.
The slot that the chain and pendulum rest in (and just a tiny glint of gold) can be seen should players think to examine the ceiling, 10’ above.