Coliseum

The Coliseum was the main structure on Metru Nui, located in the center of the city. It was where Turaga Dume's residence, and the location where sports were played. During the fall of Metru Nui, Makuta used its vast basement to store the Matoran in his plan to take control of the Matoran.

The Coliseum has a long story, and it is unknown to this day who built it and for what purpose. But whatever the case, the Turaga called Dume has always used it as his residence and place to govern the city from. In the Toa/Dark Hunter War, the Toa used it as their HQ, sending the Toa on missions from there. After the Toa won the war, sporting events resumed.

During the rise of Makuta, he used it to store the Matoran in its basements. The Toa Metru saved six, but vowed to return and rescue the others. During their absence on the island-city, Roodaka took over the Coliseum and made it the Visorak base. The Toa Metru, aided by the Rahaga, saved the Matoran and defeated the Visorak hordes.

They left the city for Mata Nui, but when it was rebuilt, they were to return. It is currently being restored by the Matoran and Turaga.