Mods used for this: Sacrosanct, RDO, EFF, SexLab Defeat (you can turn off all the NSFW features, I use it for kidnappings, executions, and hostages), and Imperious. This is, for example, where Malborn ended up after I found him alone in Windhelm following Diplomatic Immunity.

I filled the underground cages by making blood thralls out of anyone who seemed too interesting to kill but not important enough to travel with. Since my character was a Breton, I used the Shared Ancestry perk from Imperious to mimic the Bosmer Beast Tongue racial ability long enough to capture and tame a snow saber cat, which now roams the halls instead of those ugly death hounds. (As I understand it, Better Vampires has a similar feature if you prefer that mod instead.) The entrance can initially be accessed via Icewater Jetty, northwest of Northwatch Keep.

If the Dragonborn joins the Volkihar Vampires, the castle can be used as a home. The castle serves as the primary base for the Volkihar Clan. Elisif is now part of Clan Volkihar, largely because she wasn't doing much after I conquered Skyrim for my husband Ulfric, who is also under my command and a member of my court. It is a large castle that rests on a secluded island in the Sea of Ghosts. I used the Foster Childe perk from Sacrosanct to select worthy candidates to receive my gift and make into members of my court. I can't have any members of my court whose loyalty is uncertain. Castle Volkihar is a large fort on an island far northwest of Solitude, north-northwest of Northwatch Keep.The dungeon areas of the castle, most of which contain enemies, include four interior zones: Volkihar Undercroft, Volkihar East Tower, Volkihar North Tower, and Volkihar Ruins including Valerica's Study, and two additional external zones: Volkihar Courtyard and Volkihar Balcony, which is. Here what I did to populate Volkihar once I made it my permanent home:

Castle volkihar redux nexus