Tourian

From Wikitroid, the Metroid wiki

Tourian was the core of the Space Pirates' fortress on Zebes, and the lair of the Mother Brain. It is reachable through Norfair, Crateria, and Brinstar in Metroid, and reachable after you defeat the four statue bosses in Super Metroid through the ruins of the first Tourian. Many hard enemies such as Metroids, Rinkas, and Zebetites appear here.

[edit] Trivia

• In Metroid: Zero Mission, if the player returns to Tourian after beating Mother Brain, there is a green, highly corrosive liquid that has replaced the lava in Mother Brain's chamber. It is unknown what the substance is or how it got there, but it is severely dangerous to step into. In most probability, it is some sort of waste from the now inactive power systems in the destroyed area.

• It is stated by Samus in the Metroid e-Manga that Tourian is the place where the Chozo and Mother Brain make decisions that influence the Federation.