Karda Nui

Karda Nui (also known as the Universe Core or The World that Feeds the World) was a mysterious world where Av-Matoran resided.

History
Karda Nui 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 Karda Nui, 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 Karda Nui. However, instead of flooding the mainland, the water came through as a waterfall and thus all the water went into 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. Due to the Makutas invasion on the Universe Core, the Ignika started the countdown to drain all life from everything in the universe.

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

Landscape
Karda Nui was technically a swamp with Mutagen in it, although book author Greg Farshtey has stated that the inhabitants were not affected by the mutagen, mainly because it was only partially flooded and the beings could live without entering the swamps. This swamp section was known as the Swamp of Secrets. As the Staff of Artakha couldn't breach the barriers of Karda Nui, the staff couldn't restore the damage that has been done to it.

Trivia

 * There are currently no Rahi in Karda Nui,with the exeption Mutran's mutated ones.
 * Karda Nui's barriers were 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.