Grinding-Stone Tower

Grinding-Stone Tower, or , 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.

Layout
The level begins below a platform with a ? Block and a nearby pipe spawning Grrrols. A Bony Beetle is found, along with two Warp Pipes that move upwards and downwards, allowing the player to reach the next platform. More Grrrols are spawned nearby, and a platform with a Bony Beetle and two Brick Blocks is found. A moving Warp Pipe is found, and a hidden opening next to it allows the player to reach a ? Block containing a Mini Mushroom. An opening contain coins is found, allowing the player to avoid nearby Grrrols. After passing by the Grrrols, another sloped platform with a Bony Beetle on it is found, followed by two moving Warp Pipes. A series of platforms with big Grrrols on them is found, leading to the Checkpoint Flag. A group of Warp Pipes is found, with a ? Block above it and Grrrols spawning from the right. More sloped platforms and Grrrols are found, and a hidden Red Ring is found in a wall. After another platform, two ? Blocks are found, followed by multiple moving Warp Pipes acting as platforms and Grrrols. Two big Grrrols are found, followed by a platform with a Bony Beetle and the boss door on it.

A Boom Boom makes his species' last appearance as the boss of the tower. Kamek swoops in and cause the Boom Boom's arms to turn into wings, which allows him to fly and dive into the player.

Star Coins

 * Star Coin 1: A mini Warp Pipe, that leads to the area with the first Star Coin, is present at the beginning of the course, to the left. Mini Mario is required for this Star Coin.
 * Star Coin 2: The second Star Coin is hidden within a wall to the right, after a series of Grrrols.
 * Star Coin 3: Another mini Warp Pipe, that leads to the area with the third Star Coin, is present at the end of the course, to the right. As with the first Star Coin, Mini Mario is required to reach this Star Coin.

Secret Exit
Immediately after the third Star Coin is a Warp Pipe that leads to the secret exit. It opens the path to Thrilling Spine Coaster.

Enemies

 * Grrrols
 * Big Grrrols
 * Bony Beetles

Names in other languages
Grrroll-Turm des Grauens