Super Bell Subway is a track in the Animal Crossing x Mario Kart DLC Pack for Mario Kart 8. It is named after the Super Bell from Super Mario 3D World, although the track itself has no real relation to the game.
The track starts out in a hallway for a train station, then takes a U turn. After this, you'll pass through some gates and go down stairs and enter the subway. At this point, you can either ride on the ground, or drive up some ramps and ride atop the trains. After this section, you'll ride up some stairs, and take another U turn through a café. You'll reach the finish line after this.