Vault of Cloaked Midnight

The Vault of Cloaked Midnight was a temple of Vhaeraun in Ultoksamrin, around which a city of followers of the same deity grew.

Structure
The Vault of Cloaked Midnight was situated in the ruling cavern of Ultoksamrin, a 1000-ft-high grotto, a mile beneath Mount Sarengard.

The temple occupied about half of the cavern and the drow who weren't living there lived in the old dwarven clanholds for defensive reasons.

Development
The drow in Ultoksamrin were escapees from the city of Guallidurth. They were followers of Vhaeraun and fled from religious persecution at the hand of Lolth's matriarchy. They fled and built settlements in the Ultoksamrin and Forest of Mir. One of the settlements in the Forest of Mir was Allsihwann, alongside Dallnothax, Holldaybim, and Iskasshyoll. When Allsihwann was destroyed by the combined forces of Tethyr and surface elves, the drow fled to Ultoksamrin.

Despite this development, the settlement's leader Vokkrzyr Rualfren tried to invite surface elves to bolster the cathedral city's numbers, with the goal of hurting Guallidurth. Whether he had success wasn't known.

Enemies
Ultoksamrin's tunnels were divided into territories by several different races all hostile to each other, out of whom the drow were the most successful. Apart from these, they numbered the forces of Tethyr and surface elves from the surface and were also for 50 years at war with Guallidurth. The forces of Guallidurth were successful at destroying two minor temples of Vhaeraun, the Hall of Midnight Bloodshed and the Onyx Labyrinth, two decoy temples built with the specific aim of diverting attacks from Lolth's temple city.