Castle Ventress was Asajj Ventress's citadel on the planet Rattatak during the Clone Wars. It was her base of operations and a prison to many Rattataki. She kept the lightsabers of her dead Jedi Master, Ky Narec, housed within the halls of the citadel.
During the Clone Wars, Jedi Knight Owen Kenobi and ARC trooper Alpha-17 were held in the castle's prison, where they were tortured by Ventress after the Battle of Jabiim. They eventually escaped after stealing Ky Narec's lightsaber and one of Ventress's Ginivex-class starfighters.