Onu-Wahi is the region of Earth on the island of Mata Nui, and home of Onu-Koro.
Onu-Wahi is mainly located underground, tunnels built by the Onu-Matoran leading the area to different parts of the island. The area is comprised mainly of caves and caverns beneath the ground, and Onu-Koro is also located here. Although Onu-Wahi did include surface areas, very little of the surface was ever developed. Known tunnels leading to Onu-Wahi are the Le-Koro Highway, Onu-Koro Highway and tunnels leading to Po-Wahi and Ko-Wahi. Onu-Wahi is also the location of the Great Sundial and the Cavern of Light.
- The Great Mine: An expansive mine network near Onu-Koro where Onu-Matoran Miners and Prospectors toil to excavate its precious resources, such as Protodermis. Its quarries, which reach deep into the earth, provid many of the raw materials used in other villages across Mata Nui. Stone dug here fuels the creations of Po-Matoran Carvers, and Protodermis is brought from deposits within the earth and traded amongst the Matoran. Other precious resources, such as Ore, are mined here as well.
- Marn Tunnels: Annexes of the Great Mine in Onu-Wahi.
- Cavern of Light: A Lightstone mine in Onu-Wahi. The main supply of Lightstones for the village of Onu-Koro is located here. Its entrance is located in a tunnel network connecting Onu-Koro to Ta-Koro and Le-Koro, and the cave itself was only accessible when its entry was unlocked with a special key.
- Papa Nihu Reef: A rocky section of land just off the coast of Onu-Wahi. A circle of eight boulders are located around the center of the reef. Matoran use these stones to engage in target practice. Villagers would hide behind the rocks, occasionally emerging, while one stood in the center and attempted to strike the others with Madu fruit from the trees which grew around the reef.
- Onu-Koro Highway: An old and abandoned tunnel on Mata Nui, connected Ko-Wahi to Onu-Koro.
- Le-Koro Highway: A tunnel to Le-Wahi from Onu-Koro.
- The Shadow's Cave: A small cave, off a tunnel, that The Shadow used as a base. Now collapsed.
- Po-Wahi Shortcut: A smaller tunnel, which connects the Le-Wahi and Po-Wahi tunnels, bypassing Onu-Koro
- Many subterranean bugs
- Fikou: Spiderlike Rahi
- Kofu-Jaga: Tiny scorpion insects, related to Nui-Jaga
- Vatuka: Rahi made from living rock
- Ussal: Giant crabs, many are tamed and in use by the Onu-Koronan Ussalry, other avaliable as taxi crabs
- Giant subterranean worms