The focal setting of BIONICLE's story from 2004 to 2005, rediscovered at the end of the 2003 story. A futuristic city divided similar to the island of Mata Nui (Island) into 6 elementally-themed sections, known as "Metru" districts, with a massive volcano shaped colosseum in the center. Revealed in 2008 to actually be the brain of the Great Spirit Robot.
The 6 Metru districts are as follows:
- Ta-Metru - the industrial district of Fire, and home to the Ta-Matoran, known for producing Kanohi Masks
- Le-Metru - the district of Air, and home to the Le-Matoran, home of the city's transportation chute system and busy airships
- Ko-Metru - the district of Ice, and the home of the Ko-Matoran, who study, observe, and look into the future to predict and research prophecies by reading the stars, also known for housing the massive crystalline knowledge towers
- Ga-Metru - the district of Water which is home to the Ga-Matoran, the city's learning centers and schools are located here as well as the Great Temple, the most spiritual place in Metru Nui.
- Onu-Metru - the district of Earth and home of the Onu-Matoran, the archives are located here which store many relics and Rahi from all over the Matoran Universe.
- Po-Metru - the district of Stone and home of the Po-Matoran, the city's best builders and craftsmen are located here.