From Bulbapedia, the community-driven Pokémon encyclopedia.
The Navel Gym (Japanese: ネーブルジム Navel Gym) is the official Gym of Navel Island. The Gym Leader is Danny. Trainers who meet his challenges receive the Sea Ruby Badge.
The Navel Gym made its only anime appearance in Navel Maneuvers.
The Navel Gym isn't a building, and instead spans the entire mountain on Navel Island. Danny makes Trainers participate in several mountaineering challenges, including scaling the mountain without the aid of any Pokémon. Natural geysers must be frozen and crafted into bobsleds for racing down the mountain. There is no battling involved at this Gym.