Chamber of Krasus

Krasus, a red dragon and one of the six members of the Kirin Tor, resided in an elvish sanctum that was located in a secluded grove. In Day of the Dragon, Krasus sensed "powers" lingering below even the deepest of the chambers, where a pool of strange water existed with a golden gemstone sat in the bottom.

He would rarely drink from the pool to restore his strength, but oddly, the pool would reject all forms of cups and containers and thus, Krasus had to resort using his hands. When he stared into the pool, he saw odd shapes, which were at times "silvery fish," and at others still, a human torso, legs, or arms.

Aside from being "elven", both the pool and the sanctum are of unknown origin, as is the identity of the powers in the chamber's depths.

During the aftermath of the Third War, the lair was already moved to another location.

Speculation
It is possible that this chamber is located in the Tirisfal Glades where the Council of Tirisfal was said to meet.

Due to the elvish nature of the structure, it is possible that Dath'Remar Sunstrider built it when the high elves first landed upon Lordaeron. The high elves may have abandoned this and simply struck it from widely recorded history, so as to forget the disturbing events that occurred during their time there.

Building off the speculation above others have suggested the chamber may be found somewhere in the unexplored lands west of the Tirisfal Glades.

Regardless, the pool, the citadel, and the grove are of a mysterious nature, and the questions of what it truly is, what is it for, and who made it still remain to be concretely answered. With Korialstrasz's death, it is likely these mysteries will remain unsolved.