How to find it.
Bloodcrust Cavern is a small cave east of Castle Skingrad, and is populated by a small band of vampires.
South of the cave the ancillary ruins of Silorn are visible. There are no alchemical plant in the area.
Rooms
There are a handful of chests with little loot of value and only one locked chest containing a weak magic item. That plus a few other magic items which might drop is the extent of the loot for the place.
Overall the cave is an easy fight but if several of them manage to tag team you at once you will have a great deal of trouble fighting them off. You may also be infected with Porphyric Hemophilia while fighting the Vampires here.
Enemies
They are generally a mix of vampire crusaders, warriors, mages, and agents. The mages tend to summon headless zombies and shoot fire and lightning spells from a distance, then run deeper into the cave if you approach them. The melee types are simple enough, casting a few defensive spells and charging into combat. The Agents shoot you with bows until you approach them and then switch to melee weapons. The vampires are also a good way to get the current leveled weapons and armor.
One of the vampires (a Redguard swordswoman) is more sociable than the rest and will talk to you if she's not angry with you. She has little to say however.
Quests
These quests involve the Bloodcrust Cavern in some way: