One of the Ambient Structures from Katters Structures.
A ruined stone fortress that is overrun by Pillagers.
For more information on the design, there are some books from the Villager and Therons perspective explaining why it looks like it does.
The main blocks are :
Iron ... a lot
Skyhold, will naturally spawn in Rivers and their corresponding Biomes O' Plenty and Terralith Biomes.