Onu-Metru was created along with the other districts by the Great Beings. It was populated by the Onu-Matoran who began building The Archives under the Metru and eventually all of Metru Nui. After Makuta Teridax unleached the virus on Mata Nui and took over the Matoran Universe, Onu-Metru was heavly damaged by the Great Cataclysm and it's Rahi exhibits were freed. Visorak later occupied the Metru and caused more damage. The Staff of Artakha later repaired the damage but it was again destroyed when a large chunk of Aqua Magna hit Teridax in the head.
Onu-Metru's surface was rocky and barren and was mainly used for houses and for storage. Underneath the streets was home to the archives wich was home to Rahi exhibits and records.