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 was featured from Overjoyed! to Pace - The Final Frontier!.
Brandon moved his facility, the Battle Pyramid, to Fennel Valley to search the local ruins for a rare Pokémon, just prior to Channeling the Battle Zone!. After solving the ruin puzzle to reveal an ancient tablet, Brandon eventually caught the rare Pokémon, a Regice, by Pinch Healing.
After learning of the Battle Pyramid's relocation, Ash and his friends reached the valley in Overjoyed! for Ash's next chance to obtain the Brave Symbol. He lost to Brandon in his first rematch, though the group decided to stay in Fennel Valley for further training until Gathering the Gang of Four!, where Ash challenged Brandon again and finally won his final Symbol.
There is a very luxurious Pokémon Center with a fitness studio, hot springs, battlefields, and even a Contest Hall. The Nurse Joy of the Pokémon Center is a fan of both Pokémon battles and Pokémon Contests. She was also a former Pokémon Trainer. Due to this, she had a battle with Ash on one of the Center's battlefields. 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