Mangaia was one of a number of lairs belonging to Makuta. Mangaia was located beneath the Kini-Nui. One of the major features of Mangaia was a huge stone gateway so heavy no Toa or group of Toa could lift it. Only Takutanuva, the merged being formed from Makuta and Takanuva, was able to open this door. The door led to the shores of a protodermis sea, beyond which was the city of Metru Nui. Mangaia contained a pool of energized protodermis, which Makuta used to create Rahkshi from Kraata. The same pool was responsible for the creation of Takutanuva.
An enormous mask stared sightlessly from a cavern wall. Makuta once talked to it as if it were his brother Mata Nui.
Makuta's lair was deep beneath the surface of Mata Nui. No hint of light had ever penetrated it. On one wall of the chamber was an enormous mask, a carved image of the face of the Great Spirit, Mata Nui. Makuta talked to it as if it were his brother, Mata Nui.
When approaching the lair from the silver sea, just above the waterline was a stone terrace. Beyond that was an ancient gateway, clogged with stone after story year 2003. Past this gateway was the remains of Makuta's lair. The stones were the shattered pieces of the huge stone door that once stood there.
Located beneath Kini-Nui, Mangaia was one of many lairs that Makuta Teridax had in the area. It was from here that he directed his Rahi and Rahkshi attacks against the Matoran. Metru Nui could be reached by raising an incredibly heavy stone door in Mangaia.
The Order of Mata Nui destroyed the energized protodermis pool in Mangaia.
Makuta's lair was located at roughly the same depth as Metru Nui.
The combined strength of all of the Toa Nuva sharing the powers of the Pakari Nuva would not be enough to lift the gate in Mangaia.
The gate in Mangaia was probably not constructed by the Brotherhood of Makuta.