If you're smart enough to not be fooled by the facade of bushes and plants, or are apart of the Pokemon Hunters, you'll find an opening in the side of the cave walls. Follow the tunnel, and you'll find a door. Open it, and viola -- you're in the Pokemon Hunter HQ! Hunters come here to receive their starters, missions, sleep and whatever else -- so long as they're not goofing off.

The hideout itself goes down four floors, with the laboratories to receive your starter being on the third. You can ascend or descend the floors via stairs or elevator. There are obviously no windows, so the light inside is all lightbulbs.