The tomb of ancient key open Tomb dungeon.
The Tomb of the Ancients is an high-level dungeon whose portal has a guaranteed (as of X.31.9.3) chance of dropping from Grand Sphinx event boss, which spawns once per realm. The portal stays open for 30 seconds.
The Tomb is a source of the rare Potions of Life and powerful untiered rings. The dungeon has several hazards, including indestructible turrets that cause various status effects, quicksand that slows movement the longer players are in it, powerful enemies, and a highly strategic boss fight.