Mountains' Graveyard

Madara Uchiha possess a headquarters that also serves as a stronghold for his organization, Akatsuki in a location called Mountains Grave. Inside is a laboratory, where he keeps a massive storage of eyes, as well as performed a transfer of Sharingan from Itachi Uchiha to Sasuke Uchiha. Also, the Demonic Statue of the Outer Path rests inside a room, though it can be summoned to elsewhere if needed, as Nagato did so in the Land of Rivers hideout. Deeper inside the headquarters is where Madara cultivated the cells of Hashirama Senju to access his powers, as well as to create an army of Zetsu.

Outside of the main gate of the headquarters is a large bone structure, where Sasuke sat on once to think about his past with Itachi. The outside is surrounded by walls of the headquarters building itself.

Kabuto Yakushi approached this place to offer (or rather blackmail) Madara into an alliance, but he left a trail of corpses to allow Anko Mitarashi and her team to the headquarters.