A large grandfather clock, affixed into the very stone itself, ticks away here.
Observant characters might notice that the time on the clock looks like it started
the moment the Adamantium Door was opened. The clock radiates faintly of magic.
There is also a large red lever here, with some Ancient Draconic inscribed over it.
Naturally, it says "Do not pull this lever". The lever radiates magic a bit more
strongly, and detects for trap.
Inevitably, the party will pull the lever. When they pull the lever, the clock starts
winding backwards, one second for each minute it went forward. An explosion ensues,
10d8 fire and shrapnel damage, reflex save DC20 for half. The clock will be gone,
revealing a carving on the wall, "I told you not to pull the lever".
The only way out of here is to go back along one of the three
passages..