Looks like a Necropolis castle used to be inhabited by humans, but it was transformed.
And what is that dragon's mouth?
"Necropolis Fortress, recently built in a beautiful valley in the territory of Heresh. Not the best omen..."
As for the mouth, it could be the entrance to a dungeon. Or something else. I'm much more interested in the purpose of the levitating purple stone near the fortress. It has a distinctly dark elf vibe.
Bow down and hear our cry,
Our earthly rulers falter,
Our people drift and die,
The walls of gold entomb us,
The swords of scorn divide,
Take not thy thunder from us,
Take away our pride.
G.K. Chesterton: English Hymnal