The Sand Tomb

From Mario - Wiki on Neoseeker

This stadium is in the desert. In the middle of the stadium the ground is fine and you can run at a normal pace, but Thwomps are there, so you may get squashed. You can run down the sides of the stadium, the disadvantage though is it slow as you are running on sand, however it has no Thwomps to squash you. Both routes are equally hard, the one you pick depends on what team you have.