This is the third area in Pikmin: Distant Planet. You unlock it after you find the Mechanic's Sensor. It is an odd area, almost like a big cave above-ground without a ceiling. It's a large clearing in the forest on the World Map. Actually, it is the area around the edge of the entrance to The Forest Navel from the first canon Pikmin game! That would explain the odd surroundings. The ground is mostly rocky with sand and reservoirs, similar to the terrain of The Forest Navel. Incidentally, the underground portion of the area where the dungeon entrances are located has similar types of terrain that The Forest Navel did, as well as the same music. Half of the time, there will be rain of varying intensities in this area, causing flooding and mudslides, and water flowing in different directions