Valley of Ryūkotsusei

The is where Ryūkotsusei resided until he was sealed by Tōga, after which he lay dormant until he was freed by Naraku and defeated by Tōga's youngest son, Inuyasha.

Inuyasha's older brother, Sesshōmaru, later visited the Valley of Ryūkotsusei along with Jaken and Rin.

Trivia

 * In the second ending, "Fukai Mori", Sesshōmaru is seen visiting the Valley of Ryūkotsusei and reflecting on his father's legacy. This happens before Sesshōmaru and Inuyasha's first battle for Tessaiga due to Sesshōmaru shown to still have his left arm at the time.