Just another trap in the 4th level. It's an example of my favorite style, the kind the players willingly set off.
8. Liquid Loot
Floating in the center of this room are three rings of blue superconducting metal. They are nested within each other, and rotate slowly in three dimensions around a 1’ wide sphere of gold. Anyone approaching will feel the heat coming off the rings and the sphere – and in fact the sphere is molten, although that will not be obvious.
Jamming a sword, 10’ pole, or other object into the rings will merely cause them to stop spinning – they will resume once the obstruction is removed. Note that they are powerful magnets, and a successful “force doors” check is required to remove any metal stuck to them. Further, the heat from the rings will soften most metal and burn wood – each round an item is jammed into the rings, there is a 40% chance it will be ruined.
Approaching the rings with a magnet will cause them to fly apart, doing 1d6 damage to everyone in the room as they ricochet about.
In either case, once the rings stop rotating, the molten gold within will fall to the floor, splashing all within a 10’ radius for 4d6 points of damage (save vs. paralyzation for half damage).
Once outside the rings, the gold will solidify in 1 round, and be cool enough to handle in 2 turns. It will take an additional 2 turns to pry the gold from the floor, if it has splashed all over the room. The total value of the gold present is 6,000 gp.
When nested together, the rings will resist being moved, and will heat any metal in the center to 2000° F. Apart, they are simply strong magnets. The rings are worth 10 gp apiece if sold separately, and 100 gp if sold together.