Spirit Cave takes place in a tiny cave, with a small lava pit and scary faces all over the walls. It's very short in matter of length, since the only seen way is a 360º road around the cave. It was probably made for physics testing.
Its mesh was found at the source code, inside a folder called POO, which also contained BMP and TGA files of its textures. Its real name, Spirit Cave, was inside the leveldat.cpp file of the canned folder, available in the same source code. In there was also discovered that the track data directory was called cave.