Karda Nui

The Universe Core was a mysterious world where Av-Matoran resided.

History
The Universe Core was colonized by the Av-Matoran, or the Matoran of Light. The current status of the land and its inhabitants remains unknown as of now. During the Av-Matoran's colonization of the Universe Core, the Toa Mata were assigned to guard the region. About 100,000 years ago, the Av-Matoran left the core because their work there was done. After the Toa Mata were chosen to be Great Spirit Mata Nui's personal guardians, they also left the core. When Voya Nui rocketed upwards from the mainland, it ripped a hole in both the mainland and the Universe Core. However, instead of flooding the mainland, the water came through as a waterfall and thus all the water went into the Karda Nui instead, creating the Swamp of Secrets. The hole in the dome of the core was sealed when Voya Nui returned to it's former position. The Ignika was used here by Toa Mahri Matoro, reviving Mata Nui from death while killing the Toa.

Recently, a number of Makuta have invaded the core. The Order of Mata Nui is relying on the Toa Nuva to prevent the invasion, and will provide them with any available help.

Location
The Universe Core is located right underneath the Mainland and is protected by powerful shields, which also prevents the Staff of Artakha from repairing it. It is around the same size as the main land, and it is located within it's own dome. The Universe Core is located a bit deeper into the planet then the rest of the Matoran universe.

Landscape
The Universe Core is technically a swamp with Mutagen in it, although book author Greg Farshtey has stated that the inhabitants are not affected by the mutagen, mainly because it is only partially flooded and the beings can live without entering the swamps. This swamp section is known as the Swamp of Secrets. As the Staff of Artakha cannot breach the barriers of the Universe Core, the staff cannot restore the damage that has been done to it.

Trivia

 * There are currently no Rahi in the Universe Core.
 * The Universe Core's barriers are strong enough to hold back the power of the Staff of Artakha and stop the Toa Nuva from accessing their Toa Suva, thus preventing them from switching masks.