Lake of the Staff of Two Heads

The Lake of the Staff of Two Heads is an additional location hidden not far from Toga's tomb in the Border of the Afterlife, which also happens to be connected to, as its name suggests, Jaken's demonic mystical Staff of Two Heads as well as the Realm of Fire. It is a pool of clear water surrounded by lava. From there, Inuyasha and Kagome Higrashi were able to keep taps on Moroha as she grew, thanks to Jaken using his staff to project images of their daughter onto the surface of the pool.

It is also where Inuyasha finally realizes that the only thing that can grantee their return to the physical world is Tenseiga being called by Towa's connection with her father's powerful healing sword. It is also, where they learn of Kirinmaru's ultimate goal upon reaching the modern era.

Trivia

 * It is the third immaterial place that is directly associated with death and its varied nonphysical realms such as Limbo, Heaven, Hell and even the Spirit World itself.