After the murder of Sarcem, the head priest of the Church of Helm in Cauldron, and the theft of the wands of water control, the party began their search for those responsible. Their investigation led them to uncover the identity of Triel Eldurast, once a member of the Town Guard, until she murdered some of her fellows, apparently unprovoked, almost a decade ago. Word of their investigation got around, and within a few days, they were approached by a man who sold them a map which led to the place Triel was holed up. Following the map, they found this subterranean ruin at the bottom of a long round lava tube.
Within, they found the remaining members of an Ebon Triad cell. Triel, a halfling wizard named Skaven Umbermead, and a gnoll heucuva cleric called Tarkilar, all of whom they summarily slew. They recovered most of the wands of water control, but an invisible tormentor escaped with the last wand.
This subterranean ruin is now the base of operations of Phantasm.