From Bulbapedia, the community-driven Pokémon encyclopedia.
Bamboo Hill (Japanese: バンブーヒル Bamboo Hill) is an anime-exclusive location in the Alola region, found on Melemele Island. It appeared in Rise and Shine, Starship!.
In the episode, Sophocles went camping there with his parents and Togedemaru. During that time, he came across a Celesteela, which was stuck in the ground. The next day, after informing his classmates, they went to see Celesteela. With the help of a group of Grubbin, the group began to excavate around Celesteela. Sophocles believed Celesteela to be the Celestial Starship from legends, but the others believed it to be an Ultra Beast.
They returned the next day after learning from Lusamine that it was indeed an Ultra Beast. Attempts were made to catch it in a Beast Ball, but all of them were unsuccessful due to its large size and the fact that it was still rooted down to the ground. After protecting Celesteela from Team Rocket, the Ultra Guardians were able to create a safe area for Celesteela to launch back home.
Pokémon seen at Bamboo Hill