* The Pokemon League: This is the final challenge of the game, located in Snowpoint City, and is where you battle the Elite Four and Champion Cynthia. It has a luxurious, mansion-like design.
* The Veilstone Mansion: This is located in Veilstone City and is the home of the wealthy Veilstone Department Store owner, Mr. Backlot. You can explore this mansion and even get a special prize.
* The Eterna Mansion: Located in Eterna City, this mansion is the home of the former Champion, Flint. You can find him here, and it's a place where you can access certain areas and even find items.
If you have another location in mind, please describe it further, and I'll try to help you find it!