Muramasa's Fortress

Muramasa's Fortress is a secret stronghold, hidden in a giant forest, that is used by the Muramasa Neikan. It is unknown whether this lab is located in the Human World, Soul Society, or some other dimension as of yet. Muramasa uses his spatial manipulation to get to it at any time. The base is the location of his laboratory, where he has carried out numerous human experiments as well as holding cells for his prisoners. The fortress is actually much larger than it seems as there exists a large system of rooms and catacombs beneath the surface. The walls of the fortress are made out of Sekkiseki, preventing outsiders from being able to float or fly in and around the fortress.