Vault of Cloaked Midnight

The Vault of Cloaked Midnight was a temple of Vhaeraun in Ultoksamrin around which a settlement of followers of the same deity grew. It was led by Vokkrzyr Rualfren, a cleric of Vhaeraun.

Structure
The Vault of Cloaked Midnight was situated in the ruling cavern of Ultoksamrin, a 1000-foot-high (300 meters) grotto, a mile (1.6 kilometers) 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 Ultoksamrin and the 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 to hurt Guallidurth. Whether he had success isn'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, their enemies also included the forces of Tethyr and elves from the surface, and Guallidurth, with whom they had been at war for 50 years by 1370 DR. 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 purpose of diverting attacks from Lolth's temple city.