Underground

The Underground appears in a few episodes of BFDI, and it is usually accessed by digging downward or a heavy impact towards the ground.

In Are You Smarter Than a Snowball, Tennis Ball, Eraser, and Woody are stuck underground.

In Get Digging, Fries orders Nickel, Bomby, Dora, Yellow Face, and Rocky to get digging, and they dig deep underground.

In Getting Teardrop to Talk, Stapy and Marker dig down underground, and Dora does the same, and digs up a container of Cyanide.