Floating Castle was a Disney-Created featured toy box. It was featured at the launch of Disney Infinity on 8/18/13. As can be inferred by the name, the toy box depicts a floating castle.
Rail grind up into a floating castle and battle your friends for the throne in this royally awesome Toy Box.
This toy box was also refeatured on 11/27/13 with the other Week 15 Featured Toy Boxes. Both Floating Castles are still up and downloadable. They are seemingly the same, except that the new version no longer has the Frozen Flourish Terrain, having changed it to the regular Disney Infinity Terrain.
Only one of these versions still shows up on the Disney Infinity website.