Unakite Town has a secret gym during the events of Pokémon Gamma Ray (it does not appear in IR/UV, having been established in the intervening 5 years). It is the seventh gym, specialist in Ground-type Pokémon and headed by Samuel, the leader of a gang of 'underground, anti-establishment' teenagers. It is required to have TM28 (Dig) and HM04 (Strength) before accessing the gym. To get to the gym is a Regi-like puzzle: on the top tile 2nd from the left, use Dig, then use Strength to clear out the boulder to the north, then you can access this gym.