Mahri Nui was a Matoran city that broke off the island of Voya Nui and sank beneath the sea several centuries ago. In the years after Voya Nui rocketed to the surface of the ocean, molten protodermis cooled to form an additional segment of land. The Matoran residents of the island built Mahri Nui on this land, which was by nature unstable. After a few centuries, it broke off and disappeared between the waves. It landed on top of a fortress built by Ehlek, crushing it, and also disrupted the Fields of Air, releasing air bubbles. The surviving Matoran of Mahri Nui were able to use this air to sustain their own lives and to resist the mutagenic properties of the seawater. In the years that followed, the Matoran surrounded their homes and building with large air bubbles, domesticated Hydruka to harvest air, and did their best to survive. Mahri Nui rested in the center of the outer regions of the Pit. It was often menaced by sea predators that served the Barraki. Mahri Nui was connected to Voya Nui by a stone cord which contained a labyrinth of tunnels. The Matoran defended Mahri Nui by using launchers that fired solid air bubbles.
Mahri Nui was able to survive the Barraki for so long because Pridak was practical. He saw no reason to kill Matoran if there was nothing to be gained by it.
The sunken village of Mahri Nui lay beneath a saltwater ocean, the same ocean which surrounded the islands of Voya Nui and Mata Nui. However, in the depths of Mahri Nui and the Pit, the waters were quite different, having both corrosive and mutagenic properties that affected both living and non-living things. It was an extremely difficult place in which to survive. Some beings, like Botar, had a natural immunity to the environment of the Pit. Most, however, needed to take special precautions against prolonged exposure to the waters.
There were two main ways to reach Mahri Nui: down through the Cord from Voya Nui, and up from the Matoran universe through the original Pit. Although it was possible to reach Mahri Nui by traveling through the ruins of the prison and up through the black water, it was not recommended. The Order of Mata Nui advised travelers to Mahri Nui to wear a Kanohi Kaukau or else stop by the Fields of Air.
The village of Mahri Nui rested on an inverted triangle of rock, which was wedged between a pair of curved pillars of stone. If it had ever been dislodged, it would have tumbled end over end into the black water, dooming all of the Matoran living on it.
As far as the Order of Mata Nui could tell, when Mahri Nui sank, its landmass collided with another one already there. The result was a fusion of the two, explaining why some of the natural terrain was already aquatic. It landed on a pre-existing piece of rock, crushing a Barraki fortress in the city.
Mahri Nui's landmass contained a number of interesting features, including the Fields of Air, the Pillars of Salt, and the Octo Cave. The Fields of Air teemed with plants which the Matoran called "airweed," which produced bubbles of air which could be combined to form larger ones. The Matoran used hydruka to harvest air from the Fields of Air. They used this air to create large bubbles around the buildings of Mahri Nui and also smaller, personal air bubbles for Matoran who ventured outside of the city.
Mahri Nui itself was a medium-sized Matoran village, unique in appearance because of the large air bubbles over its buildings. Important places in the village included the Throne of Vision, the Sanctuary, the Fortress, and the memorial to Matoran who had fallen victim to sea predators.
Mahri Nui landed right in the midst of the Pit.
The Matoran of Mahri Nui, like the Matoran of Voya Nui, came from the group of Matoran first shipped to Karzahni and then sent afar to Voya Nui in the mainland. At first glance, they appeared not to be related to the Matoran of Voya Nui, since they were taller and stronger, showing none of the signs of Karzahni's tampering. When Mahri Nui sank, their initial exposure to the mutagenic water so far below the surface reversed many of the adverse changes Karzahni had made. It also destroyed or damaged many of their weapons, although at least some continued to function.
The Mahri Nui Matoran were survivors. They had learned how to take care of themselves and protect themselves in a hostile environment. They knew to wait for the "safe hour," when no predators were around, to tend the fields of air. They even befriended strange beasts called hydruka, who harvested the air bubbles for them.
Mahri Nui was a part of Voya Nui that broke off during the Great Cataclysm [sic]. It sank below Voya Nui into the dark waters of the Pit and was later destroyed when Voya Nui returned to its place on the continent. It no longer existed at the end of story year 2008.
- Council Chamber/Matoran Council Chamber
- The Fortress
- Matoran Holy Sanctuary/The Sanctuary
- Throne of Vision