There are a ton of things to unlock in Playboy: The Mansion, based on your various actions. This is the complete list of what to get and how to get it in Mission Mode. The requirements are different for Freeform Mode, but all items are still attainable no matter which mode you are playing.

Clubhouse - Unlocked after completing Mission 5
Grotto - Unlocked after inviting the agent to the special party in Mission 4
Pool - Unlocked after completing Mission 1