|Former Residents||Rahi, Onu-Matoran|
|Location||Northern Mata Nui|
Onu-Wahi was the underground region of Earth on Mata Nui. It largely consisted of a network of tunnels, caves and mines beneath the earth, and was the location of Onu-Koro, the village of Earth and home to the Onu-Matoran, Turaga Whenua and Onua.
When viewed from above, Onu-Wahi appeared to be nothing but barren, rocky terrain. However, underneath this rocky roof was a massive network of tunnels and caves large and small. Many of these tunnels extended to other regions of Mata Nui (with the sole exception of Ga-Wahi, and their convenience allowed for many traders to come from many villages to sell their wares - whether they be Po-Matoran carvings, Ta-Koronan-made torches or even fresh-caught Ruki fish imported from Ga-Koro.
The underground region was also ideal for Onu-Matoran mining, with the earth yielding abundant quantities of valuable minerals and resources such as ores, lightstones and protodermis. One of the largest ones - aptly named the Great Mine - went so far down that it reached the very bottom of Mata Nui, and had multiple levels around its sides.
As prosperous as Onu-Wahi was, being underground it was also very dark - thus, it was necessary for Matoran-inhabited/travelled areas to be lit by lightstones (or torches, if lightstones were unavailable). The region was so vast that many of its tunnels still remained unexplored, and were often inhabited by dangerous dark-dwelling Rahi such as the vicious Kofo-Jaga and the mysterious Vatuka creature. It was not uncommon for an unfortunate miner to be digging and unwittingly break through into an entire nest of the fiery scorpion Rahi; thus, Turaga Whenua often had to be on hand with his Drill of Onua to detect such nests. However, Onu-Wahi was also home to some friendly Rahi - the naturally-affectionate Ussal was chief among them, and were often kept as pets. The loyal crabs were also used for transport and helped with mining. The Ussalry, Onu-Koro's primary military force, also used the Ussal crabs as mounts.
While the Onu-Matoran were able to drain much of the water after the Gahlok attack, many of the lower levels of Onu-Wahi remained flooded, and could only be accessed with an Air Bladder or two on hand.
Onu-Wahi was created on Aqua Magna during the Great Cataclysm, when Mata Nui was rendered comatose by Makuta. After he collapsed face-up, into the seas of Aqua Magna, his camouflage system malfunctioned, creating an island over his submerged face.
When the Toa Metru first scouted the island to pick the locations for the Matoran's villages, this underground region would come to be known as Onu-Wahi after Whenua discovered the system of caves. When the Matoran of Metru Nui were later brought to Mata Nui, the now-Turaga Whenua and the Onu-Matoran chose a particularly enormous cavern as the main site to built their new village of Onu-Koro. Over time, the Onu-Matoran built numerous mines around Onu-Wahi, as a means of harvesting the precious minerals abundant in Onu-Wahi.
The Dark Times and the Quest for the MasksFor a while, the Onu-Matoran enjoyed peace and prosperity in Onu-Wahi; however, after a year of peace Makuta returned to plague the islanders of Mata Nui, enslaving the island's Rahi with infected masks and using them to attack the villages. After 900 years of Makuta's shadow, a wandering Matoran accidentally summoned the Toa Mata's canisters to the island. One such capsule, carrying the Toa Mata of Earth, Onua, washed up on Onu-Wahi's beach. After awakening and rebuilding himself, he travelled deeper into Onu-Wahi, eventually stumbling upon the village of Onu-Koro. Here, he met the village's Turaga, Whenua, who informed him of their plight, the Toa's destiny to save them from said plight, and the Great Kanohi masks hidden around the island they would need to collect in order to do so.
During the Toa's quest for these masks, the Matoran of Onu-Wahi would be plagued with a series of problems - one such problem was a magma pump leak in one of the Onu-Matoran's biggest lightstone mines; the magma flooded the tunnel, preventing the miners from reaching the other side to mine more lightstones. As a result, lightstone supply ran short in the other areas of Onu-Wahi, forcing Onu-Matoran to rely on inferior torches for lighting. As an additional consequence, most of the miners went on strike, refusing to work in the insufficient light. Another problem surfaced when miners working in the lowest level of the Great Mine came across a Wahi-spanning layer made of some unknown organic substance that could not be penetrated by any form of digging equipment, which was topped by a strange disk covered with strange symbols. Fortunately, Takua happened to venture again into the region of Earth. First, he managed to cross the magma flood on a Lavaboard given to him by Turaga Vakama and activate the pump on the other end, draining the magma. Now that the Cavern of Light was accessible, Onu-Wahi could be lit once more, and miners were able to resume work.
Later, he consulted the Ga-Matoran astrologer Nixie about the strange disk; she identified it as a sundial, and gave Takua a gnomon she had found in Mount Ihu. Returning to the site of the giant sundial, Takua fitted the gnomon into its center and used his lightstone to cast a shadow on the sundial's four-o'clock mark - this caused the sundial to somehow open up, forming a passageway down through the layer and into a strange white chamber with a pedestal in its center topped by a hovering gold Hau.
Later, Tahu ventured into Onu-Wahi in search of Great Kanohi, and happened to come across a Kanohi Mask of X-Ray Vision that was hidden in one of Onu-Wahi's deepest caves, at the end of a long narrow bridge spanning a deep chasm.
After the Battle of Kini-Nui, this mask suddenly disappeared, and Onepu was sent to summon Takua. Riding back to Onu-Koro on the Ussal crab Puku, Takua returned to the strange chamber, and discovered after pressing a button that appeared in the now-empty pedestal's side that the sundial was actually an entrance into the shadowy lair of Makuta.
The Bohrok War
When Makuta first awakened the Bohrok swarms, Onu-Wahi was attacked by a swarms of Gahlok and Nuhvok; the Onu-Matoran were forced to evacuate the rapidly-flooding caves, but three ended up being trapped in a cave: Onepu, Taipu, and the inventor Nuparu. The three Onu-Matoran were initially frightened when they saw that the cave also contained a Gahlok, but quickly realized that it was inanimate, due to the loss of its Krana. Taipu and Onepu quickly set about trying to dig their way out, but Nuparu examined the deactivated Gahlok, and was suddenly struck with an idea. Enlisting the help of his two fellow Onu-Matoran, Nuparu disassembled the mechanical shell and, using the pieces from it and other spare parts, invented a vehicle that could knock the Krana from Bohrok with its powerful arms. Dubbing his invention "Boxor", Nuparu manned its controls and broke out of the cave. Confronted by a group of Gahlok, the Boxor made short work of the bug-like machines.
Discovery of the Mask of Light and the search for the Seventh Toa
After the Bohrok-Kal]] crisis, the Ga-Matoran Hahli ventured into Onu-Wahi to compete against the Onu-Koro Kohlii Team. Following the discovery of the Mask of Light, Takua would return to Onu-Wahi, this time with his friend, Jaller, during their quest for the Seventh Toa.