Procedurally generated Crypts, Castle ruins and Cave-lairs... (Dungeons! & Endless Gameplay)
The game randomly generates ruins and resource nodes already. My suggestion, to add more exploration and repeatable content, is to allow shared (PvP or Clan mates) or instanced (PvE) mini-dungeons (or huge!) that are spawned as entrances in the fixed world map.
These could be cave/lair entrances on hillsides, crypt doors among ruins (filled with horrors, traps and ancient vampire treasures!) and maybe even more intact Vampire Castles that have long been abandoned to explore (also filled with horrors, traps and ancient vampire treasures!) and potentially refurbish into a new home.
Treasures you say? Maybe these could be protected by a deadly guardian to justify juicy rewards for the cunning Vampire
-Rare cosmetics/skins for Vampires and their minions (You should look up my other post on npc minions*)
-Tomes for new/rare Spells
-Tomes for Castle Cosmetics
-New Forms & Skins for your Forms
-Weapons & Armour, rare/unique etc.
-Tomes to learn new Undead to summon*