From Bulbapedia, the community-driven Pokémon encyclopedia.
Fennel Valley (Japanese: フェンネル谷 Fennel Valley) is an anime-exclusive location in Kanto that is first visited in Overjoyed!.
It is visited by Ash and his friends because it is the second location of the Battle Pyramid which Ash has to battle to obtain the Brave Symbol. He loses to Brandon but keeps training in the valley until Gathering the Gang of Four!, where Ash challenges Brandon again and finally wins his last Symbol to become the Battle Frontier Champion.
There is a very luxurious Pokémon Center with a fitness studio, hot springs, battle fields, and even a Contest Hall. The Nurse Joy of the Pokémon Center is a fan of Pokémon battles and Pokémon Contests. She was also a former Pokémon Trainer. Due to this, she had a battle with Ash in one of the Pokémon Center's battle fields. She was able to defeat Ash and his Corphish. After the battle, she automatically took care of Corphish.
In The Unbeatable Lightness of Seeing!, May and Drew had a two-on-two Contest Battle in the Pokémon Center's Contest Hall, with May using her Combusken and Beautifly against Drew's Roselia and Butterfree. The battle was judged by Professor Oak and Scott while Nurse Joy served as the announcer. Drew emerged victorious after May's Pokémon were knocked out.
Pokémon seen in Fennel Valley