Metru Nui was located far beneath the surface of Mata Nui. It sat in the center of a silver sea of protodermis.
Mini-dams in Ga-Metru held back tides of protodermis so as not to overflow the metru's canal system.
Metru Nui was surrounded by a silver sea of liquid protodermis. Its waters were ice-cold.
After the battle for Metru Nui, the Brotherhood ships had sunk to the bottom of the silver sea [mentioned by name].