Murder-hobos, scavengers, and looters are drawn to the lure of unguarded gold. And the mythical image of being rained with gold and treasure may be too much to resist....
The trap is baited with runes along passages or elsewhere declaring that anyone entering a particular room will be showered with gold. Those blinded by greed will not realize it is a warning, a literal mis-translation.
The trap is a typical, empty, 10x10 room. Gold flecks and spatters may be observed scattered on the floor.
Anyone looking up will notice a grid of small holes covering the ceiling. The floor is rigged to be pressure-sensitive, requiring at least 400 lbs to trigger the trap as trespassers enter the room to scavenge the "gold" detritus.
After two minutes, a warm whoosh will emanate from the ceiling, followed by rain of molten "gold" - an alloy-tinted lead melted by alchemical means.
Those caught in the molten rain will receive 2d6 burn damage, distributed between all those in the room (characters wearing metal armor and/or helms reduce damage 1 point), with 1d6 damage the 2nd round (minimum of 1 point damage per character). Additionally, removing the solidified metal that has embedded itself will cause 1d2 additional damage.