Mountains' Graveyard

is a mountainous region located at the north-most region of the land between Takigakure and Otogakure. It has dense forestry and the bones of many giant creatures can be seen jutting out of it. It is the secret hideout of Madara Uchiha and later Obito Uchiha — who assumed the alias "Tobi".

At the start of the Fourth Shinobi World War, Kabuto Yakushi managed to locate the place while also using a trail of corpses to lead Anko Mitarashi's team there as well.

About
Some time after being defeated by Hashirama Senju, Madara set up a base here. There were no entrances nor exists, as Madara was living off life support provided by the Demonic Statue of the Outer Path. White Zetsu clones were instead used to gather information from the surface world and carry out any other functions as they could travel through the earth. There were however passages that seemingly led to different countries as Madara was able to have the White Zetsu retrieve a heavily wounded Obito who was in the Land of Grass. This passage was eventually closed off on Madara's orders and later smashed open by Obito by using the powers of the Demonic Statue of the Outer Path.

When occupied by Madara, there was only Hashirama's living clone from which sprouted the Zetsu minions, the tree which grew from it and the Demonic Statue seated upon it, a large tree stump which Madara occupied and a wooden bed on a single platform. The sealed of passage also contained his Gunbai, a Kama, several giant Shurikens and cloaks hanging on the wall. Though Madara claimed there was no exit to where they were, many hidden entrances and exits had been carved out, hidden beneath the bones of dead animals, or else etched into the walls

Within the base there is also a laboratory where Tobi keeps a massive storage of eyes, as well where he examined Danzō Shimura's dead body and transplanted Itachi's Sharingan into Sasuke. Beneath the Clone of Hashirama is a flooded cavern where Tobi bread an army of White Zetsu Clones using the chakra from the Tailed Beasts stored within the statue.