ひみつきち Himitsu Kichi (Japanese), Secret Base (English)
The Secret Base is a secret area owned by the player in some Pokémon games. It can be decorated with various accessories, furniture, and dolls.
In the Hoenn games (RSE and ORAS), the player may build a Secret Base in any of various predefined spots. It may be a cave, a treehouse, or the inside of a shrub.
In the Sinnoh games (DPPt), the player may build a Secret Base by digging a cave in the Underground.