Mt. Steel is the third dungeon in Pokémon Mystery Dungeon: Red Rescue Team and Blue Rescue Team. This dungeon is unlocked after the main character and their partner save Magnemite from Thunderwave Cave, and two rescue missions have been completed afterward. After these tasks are done, a Dugtrio appears at the Rescue Team Base to request a rescue: an angry Skarmory, convinced that Dugtrio and their son Diglett were the cause of recent earthquakes, kidnapped Diglett and took him to the top of Mt. Steel.
After Skarmory has been defeated during the initial mission, it will no longer appear at Mt. Steel.