Sumo Arena/Organic Tunnels
This is an area that appears to be a traditional sumo ring, which is also connected to a series of organic-like tunnels.
Fetuses that appear to look like Sumo wrestlers, and will only appear in the organic tunnels. They will jump around through walls, and will lead you to a large room with more fetuses jumping around.
The characters on their torso have kanji writing on them. They mean "Fetus" in English, and this is why it's often assumed that the organic tunnels represent the inside of the human body.
Touching them will link to Monument Park.