This sunken village of Mahri Nui was surrounded by air bubbles, which allowed its Matoran villagers to survive. Once a part of the floating island of Voya Nui, this submerged village remained linked to Voya Nui through a stone cord.
Mahri Nui’s position was dangerous. Not only did the Matoran and their Hydruka helpers need to constantly replenish their air supplies, the village itself was perched near the lip of The Pit, a deep and unfriendly realm. The Pit was once a prison, home to all the worst beings imaginable, but its guardians were destroyed a thousand years ago in the Great Cataclysm. The Barraki and others swarmed toward Mahri Nui, which lay nearly defenceless.
But the Mask of Life, which had fallen from Voya Nui down to Mahri Nui, brought with it Toa that helped defend the Matoran and their little village. Despite battles that raged around it, the bubbled village survived long enough for the Toa Mahri to evacuate the Matoran through the stone cord up to Voya Nui.
Once the Mask of Life was safely in the Toa’s possession and the Matoran safe, they destroyed the stone cord and Voya Nui smashed through Mahri Nui.