Walkthrough: At the bottom of the well is the town of Shiveria. After landing safely, you should find a Warp Pipe that leads back out to the blizzard, more Purple Coins for the taking, and a Power Moon above a stack of boxes to the left. Head down the path in front of you, stopping by the Crazy Cap Store to obtain another Power Moon. From there, head to the end of the path to find Shiverians watching Bowser's Airship circle their stolen Frost-Frosted Cake. One top of stealing this delicacy, Bowser has also cut off the entrance to their famed racing circuit.
In order to find Bowser, Mario will actually have to find four different Power Moons that are linked to open the barriers to the race course. There will be four different paths from the main room that will actually lead to four different areas, each containing one of said Power Moons. Before heading down the first path (bottom right) into Icicle Cavern, make sure to find and obtain the other two of the Power Moons of this area. The first can be found in a mound of snow on the second floor of the town, accessed by climbing a pole and crossing to the other side. The second can be found by removing another mound of snow to find a path to another hallway containing the Power Moon.