Karda Nui

"It’s a big cave. With a swamp in it."

- Mutran, The Mutran Chronicles

Karda Nui, also known as the Universe Core or The World that Feeds the World, was a part of the Matoran Universe, and where the Av-Matoran first resided. Its name meant "Great Heart" in the Matoran language. It contained the Stalactite Villages, the Swamp of Secrets, the Codrex, and the Shadow Leech Hive.

Karda Nui was created by the Great Beings to regulate energy throughout Mata Nui's body and the Matoran Universe. This was directed by the Energy Storms. Karda Nui acted as Mata Nui's "heart."

History
Karda Nui was colonized by the first type of Matoran, Av-Matoran during the time that the rest of the Matoran Universe was being created. 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 and a massive storm was coming as Mata Nui awoke for the first time. The Toa Mata were destined to be the Great Spirit Mata Nui's personal guardians, and they took refuge from the storm in Toa canisters, where they would stay for about 99,000 years.

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. Also, most of Karda Nui's huge stalactites fell, leaving pillars with conveniently flat tops. Sometime during this, the Av-Matoran returned to Karda Nui, though the reason why is unknown.

The hole in the dome of the core was sealed when Voya Nui returned to its former position. The Ignika was used here by Toa Mahri Matoro, reviving Mata Nui from death by sacrificing himself. Though long before the hole was sealed, (and just after the Great Cataclysm) the Toa Mata were launched out through it to begin their mission to awaken Mata Nui which would take over 1,000 years to complete.

Later, a number of Makuta invaded the core. The Order of Mata Nui was relying on the Toa Nuva to prevent the invasion, and would provide them with any available help. Due to the Makuta invasion on the Universe Core, the Ignika started the countdown to drain all life from everything in the universe. Just before The Ignika awoke Mata Nui, the residing Matoran were evacuated. Karda Nui was then incinerated by the Energy Storm.

After Teridax was killed the energy storms stopped.

Location
Karda Nui was located in the "chest" of the Great Spirit Robot, right underneath the Mainland. It was protected by powerful shields, which also prevented the Staff of Artakha from repairing it. It was around the same size as the mainland, and it was located within its own dome. The Universe Core was located a bit deeper into the robot than the rest of the Matoran Universe. 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 Suva, thus preventing them from switching masks.

Trivia

 * The "Karda" from Karda Nui is derived from the english word "cardiac" (cardiac means heart).

Karda Nui