The Super Mario Princesses having fun at Isle Delfino... naked.
Other versions available:
Bikinis- http://sigurdhosenfeld.deviantart.com/art/Princess-Pool-Party-88000654
One-piece swimsuits- http://sigurdhosenfeld.deviantart.com/art/Princess-Pool-Party-Version-2-92191512
Sling bikinis- http://sigurdhosenfeld.deviantart.com/art/Princess-Pool-Party-version-3-103800301