Toa: Onua Nuva
Onu-Koro is a village of dark tunnels, caves and mines that plunge deep beneath the surface of the island. The Onu-Matoran mine protodermis, compete in Ussal crab races, and listen closely for the vibrations that warn of danger approaching. When the Matoran are in danger, Onu-Koro is a good place to hide. In the worst of times, Onu-Koro tunnels have been used to get messages from one village to another. Onu-Matoran can see in the dark and their eyes are sensitive to bright light.
Source: The Official Guide to BIONICLE