From the Super Mario Wiki
Ads keep the MarioWiki independent and free :)
Grinding-Stone Tower, or Rock-Candy Mines-Tower, is the first Tower of Rock-Candy Mines in New Super Mario Bros. U. This level is unlocked via completion of Porcupuffer Falls. Defeating the Boom Boom in this course unlocks a passage to Waddlewing's Nest and Light Blocks, Dark Tower, and the tower's secret exit unlocks Thrilling Spine Coaster.
A Boom Boom makes his species' last appearance as the boss of the tower. Kamek will swoop in and cause the Boom Boom's arms to turn into wings, which allows him to fly and dive into the player.
Immediately after the third Star Coin is a Warp Pipe that leads to the secret exit. It opens the path to Thrilling Spine Coaster.
Names in other languages