Great Barrier

The Great Barrier was an incredibly huge underground dome of rock and solid Protodermis that housed Metru Nui and the entire Silver Sea. It was here that the Toa Metru defeated Teridax in the Silver Sea. The "ceiling" of the dome had two "suns" that were actually holes in Mata Nui´s surface and "stars" (they are not normal stars). After the Great Cataclysm one hole was covered up, but later uncovered by the power of the Staff of Artahka.