From Bulbapedia, the community-driven Pokémon encyclopedia.
The Hidden Village (Japanese: かくれ里 Hidden Village) is a location in the Pokémon world. It is located in between Cerulean City and Vermilion City.
Run by Melanie, the village is a place for Pokémon who have been abandoned by their Trainers. She takes care of them until they're ready to return to the wild.
In the anime
The Hidden Village appeared in the episode Bulbasaur and the Hidden Village.
Ash and his friends stumbled across the Hidden Village by accident. They were trying to head to Vermilion City and had gotten lost. While on the way, Brock fell off a bridge and was swept away by a river. Melanie rescued him, and she brought Ash and Misty to the village.
Helping to protect the village was a Bulbasaur, who Melanie said it volunteered to guard it. Although it meant well, the Bulbasaur was unintentionally causing all the Pokémon to stay in the village since it was so safe. After saving it from Team Rocket, Melanie asked Ash if he wanted Bulbasaur to come with him. Ash agreed, and captured the Bulbasaur.
After Ash and his friends left the village, it was never seen in the anime again.
Pokémon seen in the Hidden Village
In the manga
In The Electric Tale of Pikachu manga
In the manga series The Electric Tale of Pikachu, the Hidden Village appears in the chapter Pikachu's Excellent Adventure. When Ash and Brock meet A.J. and Samurai after a performance by Duplica and her Ditto, they make plans to visit the Hidden Village, a paradise for lost Pokémon which have been abandoned by their Trainers and is supposedly run by a goddess. Deciding to seek out the Hidden Village in search of high-leveled Pokémon, A.J., Samurai, Ash and Brock head for a bus, however, Pikachu is distracted by a Squirtle shell and is separated from Ash. Remembering that Ash wanted to find the Hidden Village, Pikachu tags along with an abandoned Squirtle, Damian's Charmander, a wild boy named Tommy and his Kangaskhan mother to find the Hidden Village and hopefully reunite with Ash. Jessie and James tag along, hoping to steal rare Pokémon, but they are stopped by Kangaskhan.
When they arrive, it is revealed that the village is protected by Melanie, an ordinary girl, but because of her kindness to the abandoned Pokémon, she is seen by them as a goddess.
Seen in the village