Stone Cord

The Stone Cord was an enormous formation of hardened lava that connected Voya Nui and the sunken city of Mahri Nui. It formed shortly after Mahri Nui broke off of Voya Nui and anchored Voya Nui in one place. It was partially hollow, and Zyglak began to inhabit it. A Rahi modified to be a vehicle, called the Toa Terrain Crawler, was also found in the cord.

The Toa Inika had to travel down the cord to get to Mahri Nui in pursuit of the Kanohi Ignika. They encountered the Zyglak and also had to defeat Vezon, who was pursuing them after being defeated by them soon before. The antidermis that made up Teridax also traveled down the cord, at one point taking over Toa Matoro's body while his spirit had left it through the power of his Kanohi Iden.

Eventually, a 300-foot long venom eel by the name of Viskus, decided to wrap itself around the cord and shattered part of it, causing water to flood in. The Toa Inika took their chances in the open ocean, being transformed into Toa Mahri by the Mask of Life. They defeated the venom eel and went after the mask.

A robotic guardian of the former prison known as the Pit called Maxilos (his body controlled by the Teridax) informed the Toa Mahri that to save the life of the dying Great Spirit, they would have to sever the cord, causing Voya Nui to sink and Mahri Nui to be smashed, killing every Matoran in both of those places.

The Toa Mahri, however, led the Matoran living in Mahri Nui up the Stone Cord to Voya Nui's caves where they would be safe, and met Axonn leading the Matoran of Voya Nui to the same caves. He gave them the Toa Terrain Crawler to get back to the outside of the cord, and they got back into the ocean and destroyed the cord with their Cordak blasters, causing Voya Nui to sink, crush Mahri Nui, and float away as if pulled by a magnetic force. The Toa Mahri followed it, even as they felt Mata Nui die.