From the Super Mario Wiki
Waddlewing's Nest, or Rock-Candy Mines-3, is the third course of Rock-Candy Mines in New Super Mario Bros. U. It is unlocked via completion of Grinding-Stone Tower or Shifting-Floor Cave, and its own completion opens the path to a red ! Switch, a spot where a Bubble Baby Yoshi resides, a green Toad House, and Walking Piranha Plants!.
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