D&D 3.0: Tales from Mystara
Tarnskeep is the castle of Baron Sherlane Halaran leader of the Barony of Threshold int he Kingdom of Karameikos. Is a small, sturdy fortress, with a single curtain wall and four towers and a large manor house. The manor has a dungeon beneath it (of the prison variety, not a lair for monsters). The keep was built by the Baron so is relatively new, but it was built in top of the ruins of an ancient major.