Welcome to the Infinity Castle Where all Demons, Twelve Kizuki Upper moons and Lower moons live and is Muzan Kibutsuji’s lair and where he rules.

The Infinity Castle is a pocket dimension consisting of lamplit wooden rooms, long halls, and moving corridors. It possesses a warped direction of gravity, allowing demons to stand upright, upside down, or perpendicularly on the walls, or move in physically impossible directions Its unusual structure and layout as Nakime's Blood Demon Art allows any structure within to shift at her will, though the castle additionally also seems to move on its own