Onu-Koro
Onu-Koro was the earth engineers' city, where underground isolation created one of Mata Nui's most self-sufficient settlements, until the Bohrok came.

Deep beneath Mata NuiMata Nui (Location)An island created by accident on the Great Spirit's face, home to the Matoran for a thousand years.'s surface lay Onu-KoroKoroThe Koros were the six elemental villages established by the Toa Metru on Mata Nui after the Great Rescue, each tied to one element and one Turaga., the subterranean settlement of the Onu-MatoranOnu-MatoranEarth-wielding Matoran of the deep who adapted to darkness and built the Matoran Universe's defensive cavalry.. TuragaTuragaFormer Toa who fulfilled their destiny and transformed into leaders. Turaga wield Noble Kanohi masks and weakened elemental powers, guiding their communities. WhenuaWhenuaToa Metru of Earth and later Turaga of Onu-Koro, formerly an Onu-Metru archivist whose career in the Archives shaped his role across the rescue of Metru Nui and the long residency on Mata Nui. led the village with quiet confidence, while Toa OnuaOnuaOnua was the Toa Mata and Toa Nuva of Earth, a quiet, deliberate warrior whose patience and underground mastery anchored his team across the Matoran Universe. served as its protector. The Great Market drew merchants from across the island, eager to trade for what the Onu-MatoranOnu-MatoranEarth-wielding Matoran of the deep who adapted to darkness and built the Matoran Universe's defensive cavalry. engineers produced. It wasn't a settlement that depended on sunlight or open sky. Onu-KoroKoroThe Koros were the six elemental villages established by the Toa Metru on Mata Nui after the Great Rescue, each tied to one element and one Turaga. thrived where others wouldn't, in the earth itself.
The Underground City#

WhenuaWhenuaToa Metru of Earth and later Turaga of Onu-Koro, formerly an Onu-Metru archivist whose career in the Archives shaped his role across the rescue of Metru Nui and the long residency on Mata Nui.'s leadership defined Onu-KoroKoroThe Koros were the six elemental villages established by the Toa Metru on Mata Nui after the Great Rescue, each tied to one element and one Turaga. as something distinct from the surface KoroKoroThe Koros were the six elemental villages established by the Toa Metru on Mata Nui after the Great Rescue, each tied to one element and one Turaga. in both culture and economy. He described the settlement as a wondrous underground city where MatoranMatoranThe most abundant species in the Matoran Universe, chosen by Mata Nui to inhabit and maintain his cosmic body. came from far and wide to trade at the great Market and admire the work of the engineers. The engineering culture of the Onu-MatoranOnu-MatoranEarth-wielding Matoran of the deep who adapted to darkness and built the Matoran Universe's defensive cavalry. ran deep and carried real prestige. They specialized in mining and construction, pulling valuable resources from the earth that supplied trade goods for the entire island. Toa OnuaOnuaOnua was the Toa Mata and Toa Nuva of Earth, a quiet, deliberate warrior whose patience and underground mastery anchored his team across the Matoran Universe. stood as protector of this underground settlement, guarding against threats that emerged from the depths of Onu-WahiOnu-WahiThe underground kingdom of Mata Nui, home to the Onu-Matoran and Toa Onua..
Under Fire#
The BohrokBohrokHive-minded mechanical creatures designed to reshape worlds, the Bohrok represent a threat the Toa Mata never expected. invasion brought the first major test to Onu-KoroKoroThe Koros were the six elemental villages established by the Toa Metru on Mata Nui after the Great Rescue, each tied to one element and one Turaga.'s defenses. When NuhvokNuhvokThe earth-dwelling Bohrok whose rigid nature made them dangerously predictable. swarms erupted from their hives beneath the earth, they attacked the underground settlement directly, seeking to overrun what lay below. But Toa OnuaOnuaOnua was the Toa Mata and Toa Nuva of Earth, a quiet, deliberate warrior whose patience and underground mastery anchored his team across the Matoran Universe. proved far more capable than the invaders expected. According to BIONICLEBIONICLE: Matoran AdventuresA 2002 GBA platformer where you play as one of six Matoran fighting Bohrok across Mata Nui's islands. Chronicles 2, OnuaOnuaOnua was the Toa Mata and Toa Nuva of Earth, a quiet, deliberate warrior whose patience and underground mastery anchored his team across the Matoran Universe.'s understanding of the BohrokBohrokHive-minded mechanical creatures designed to reshape worlds, the Bohrok represent a threat the Toa Mata never expected.'s predictable nature let him exploit their weakness: their rigid, autocratic structure made them easy to mislead. He tricked them into submission, holding the line even as other KoroKoroThe Koros were the six elemental villages established by the Toa Metru on Mata Nui after the Great Rescue, each tied to one element and one Turaga. fell to the swarms. Later, during the events of BIONICLEBIONICLE: Matoran AdventuresA 2002 GBA platformer where you play as one of six Matoran fighting Bohrok across Mata Nui's islands.: Mask of Light, new danger emerged. Three RahkshiRahkshiArmor suits powered by parasitic Kraata, Rahkshi were Teridax's most effective soldiers and among Bionicle's most visually iconic early enemies. burst through Onu-KoroKoroThe Koros were the six elemental villages established by the Toa Metru on Mata Nui after the Great Rescue, each tied to one element and one Turaga.'s walls, and OnuaOnuaOnua was the Toa Mata and Toa Nuva of Earth, a quiet, deliberate warrior whose patience and underground mastery anchored his team across the Matoran Universe. unleashed an earthquake that buried them under piles of earth, buying time for the villagers to escape.
Compiled from primary sources by Lore Fortress editorial. Reviewed by Joe Garratt, Editor-in-Chief.
Gallery

Images via BIONICLE Wiki (Biosector01)
Sources
- BookBIONICLE Chronicles 2: Beware the Bohrok — The Bohrok invasion and Nuhvok attack on Onu-Koro
- VideoBIONICLE: Mask of Light — The Rahkshi attack on Onu-Koro and scenes in the underground settlement
- GameMata Nui Online Game — Whenua's description of Onu-Koro as a center for engineering and trade
- WikiBiosector01 - Onu-Koro — Comprehensive overview of Onu-Koro's history and significance
Spotted a factual error or a primary source we missed? Email a correction. Every flagged claim gets reviewed.
Related entries
Onu-Wahi
The underground kingdom of Mata Nui, home to the Onu-Matoran and Toa Onua.
Mata Nui (Location)
An island created by accident on the Great Spirit's face, home to the Matoran for a thousand years.
Koro
The Koros were the six elemental villages established by the Toa Metru on Mata Nui after the Great Rescue, each tied to one element and one Turaga.
Onua
Onua was the Toa Mata and Toa Nuva of Earth, a quiet, deliberate warrior whose patience and underground mastery anchored his team across the Matoran Universe.
Whenua
Toa Metru of Earth and later Turaga of Onu-Koro, formerly an Onu-Metru archivist whose career in the Archives shaped his role across the rescue of Metru Nui and the long residency on Mata Nui.
Turaga
Former Toa who fulfilled their destiny and transformed into leaders. Turaga wield Noble Kanohi masks and weakened elemental powers, guiding their communities.
Mentioned in98 entries
Aiyetoro
Aiyetoro was an Onu-Matoran of Metru Nui who became a miner in Onu-Koro on Mata Nui, one of the laborers who dug for protodermis and lightstones beneath the island.
Akilini
Akilini was the principal sport of Metru Nui, played with Kanoka disks on the arena floor of the Coliseum and serving as both civic spectacle and the means by which the worth of a freshly forged disk was tested before mask-making.
Amana Volo Sphere
The Amana Volo Spheres were free-floating globes of dark energy discharged from Rahi when their Infected Kanohi were removed, absorbed for strength and healing, and gifted to Takua by the Tree Keepers of Mata Nui as thanks for curing the Vuata Maca Trees.
Azibo
Azibo was an Onu-Matoran prospector of Onu-Koro whose discovery of the Great Sundial at the bottom of Mine Shaft B opened a concealed passage into Mangaia.
Boxor
Built by Nuparu from a salvaged Gahlok shell, the Boxor was the first Matoran-engineered combat machine and a key resistance asset against the Bohrok swarms.
Cavern of Light
The Cavern of Light was the principal Lightstone source on Mata Nui, sealed behind a single Onu-Matoran key and central to the island's illumination infrastructure.
Charms
Small carved stones inscribed with the Three Virtues, the six Principles, and the six Kohlii Skills, used as keys to the six Wahi temples on the island of Mata Nui.
Climbing Claws
Pohatu Nuva's primary armament, serving as both melee weapon and traversal gear across Po-Wahi terrain until the issue of Adaptive Armor.
Dikapi
Dikapi were flightless desert birds native to Po-Wahi whose great stamina made them favored mounts for Po-Matoran scouts and messengers.
Dosne
Dosne was an Onu-Matoran of Onu-Metru who became the Mining Captain of Onu-Koro on Mata Nui, evacuated the village during the Rahkshi attack, and later returned to Metru Nui before evacuating to Spherus Magna.
Earth Shield
The Earth Shield was the elemental tool of the Nuhvok Bohrok, used to weaken soil and excavate tunnel networks beneath Mata Nui during the cleansing.
Earthshock Drills
The Earthshock Drills were the paired Toa Tools of Whenua, used to channel Earth and to excavate the tunnels of Metru Nui.
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