The Tripartite Fortress
The Tripartite Fortress is the stronghold of the dark elf house of Mogogue, a family of powerful magic-users and one of the richest families in the Underdark.
The stronghold is located to the southwest of Zenvenesne, about a two day journey through winding Underdark tunnels until the main cavern is reached. The stronghold itself sits in a cavern rivaling the size of the one that holds Zenvenesne itself, with great stalagmites which surround the sharp angles of the fortress itself. The cavern is said to be naturally on a very thin part of the plane of earth, and sometimes bleeds through with fey magical energy, which is why the Mogogues have chosen to build their stronghold there.
The fortress itself is composed of a massive dark stone tower, which rises up to the top of the cavern, and shines with an unearthly purple light. Three great wings extend on the sides of the bottom of the tower, which house the living quarters of the three distinct levels of magic-user within the family: the Apprentices, who bear little magical talent, the Adepts, who are competent at their chosen disciplines, and the Masters, who wield great power. The treasury of the house supposedly rests in a large orb at the very top of the tower. The tower is supposedly therefore exceedingly well guarded, both with creatures such as Intellect Devourers, hired mercenaries, and ridiculous amounts of traps, both magical and non-magical. In the time of a house war, as we are currently in, the fortress is liable to be near impenetrable.
The Mogogue family have traditionally been the foremost arcane minds among the drow. Their family pursues all manner of arcane magic, which means they bear warlocks, wizards, and sorcerers among their line. Their fortress’s location on a planar line means that their abilities are often enhanced, especially within their own stronghold. Their leader is a scheming matriarch named Macal Mogogue, who is unnaturally old even for a drow and has all the years of experience to match it. She has been out directing forces in raids and building projects, and is usually absent from the fortress present, which bodes well for your party. Their sigil is a black crescent moon, which they fly prominently on great banners. They feel nigh invincible after near-destroying the house of Aresne, which means they’ll be aloof. That means they’ll be easier to take out.