The Ghost Fortress is a structure added by Silver's Idea Pack. It spawns only in Ghostly Biomes, where it floats high above the Void. It is where the Lich resides with its ghostly minions. The Ghost Fortress is made out of Stone Brick.
The Lich occupies the tall tower in the middle.
There are five towers of the Ghost Fortress, four of them for Necromancers. The south tower holds Samlheim, the east Elheim, the north Niflheim and the west Wilheim.