From Bulbapedia, the community-driven Pokémon encyclopedia.
Mt. Deepgreen (Japanese: しんりょくのやま Deep Green Mountain) is a Friend Area in Pokémon Mystery Dungeon: Red Rescue Team and Blue Rescue Team. It becomes available when the player buys it for 130 Poké from Wigglytuff. It is in the Mountain Range area, and has a capacity of twelve Pokémon.
Mt. Deepgreen is a mountain filled with shrubs, grass, and other greenery. The center is lower leveled while the sides of the mountain are at a higher elevation.
A mountainous area with lush plant life and deliciously fresh air. Pokémon are happy to live in this bountiful area.