Tourian is the final region of Zebes encountered by Samus in Metroid, Super Metroid, and Metroid's remake, Metroid: Zero Mission. In each of these games, Tourian is the location of the primary antagonist, Mother Brain, as well as the majority of the Metroids. Tourian is distinctly different than the other regions of Zebes, in that it is largely composed of metal, giving the indication that it was built, rather than having naturally existed. Though bearing the same name, the Tourian visited in both Metroid and Zero Mission is not the same as its counterpart in Super Metroid.
Metroid and Zero Mission
Though their maps vary to some extent, Metroid and Zero Mission feature comparable maps, with Tourian located in roughly the same place in both. In both games, the entry point to Tourian is reached by ascending a tall shaft east of the staring point in Brinstar, and traveling westward from there. There, a barrier blocks the way, and it can only be opened by the defeat of Kraid and Ridley in their respective hideouts. After the barrier, an elevator leading down to Tourian can be accessed.
Tourian is a series of long hallways with doors of various levels blocking the way, requiring the use of Missiles to proceed. Throughout Tourian, Rinkas constantly appear to stall Samus's progress, implying a defense system.
While there are no Space Pirates in Metroid's Tourian, Zero Mission contains the bodies of dead Space Pirates, implying that they were killed by the Metroids. In the original, Metroids are always visible in the foreground, and killing them is not required. In Zero Mission, Metroids appear from the background, and must be exterminated before the next room can be accessed. This is accomplished by freezing them with the Ice Beam and shooting them with Missiles.
Mother Brain, protected by five barriers of Zebetite, several turrets, and a constant barrage of Rinkas, is the final boss encountered by Samus in Tourian. However, upon defeating Mother Brain, a time bomb is set, and Samus is required to flee through a long, upward escape shaft, leading to the surface of Zebes.
In Super Metroid, Tourian's location has changed, and it is no longer accessed through the upper areas of Brinstar. Instead, an elevator in the western parts of Crateria, which comprises the surface and top layers of Zebes, is its entry point.
This elevator shaft is sealed by the Golden Statue, and cannot be accessed until four bosses are defeated. Kraid and Ridley again stand in between Samus and Tourian, but this time, Phantoon and Draygon must also be killed in order for Samus to advance.
Super Metroid's Tourian maintains the same artificial look of the original, as well as the presence of both Rinkas and Metroids. As in the original, Metroids attack Samus from the foreground, and as in Zero Mission they must all be killed to advance.
Once all of the Metroids have been defeated, allowing Samus to advance, a more naturally-occurring section of Tourian is accessed. Native plants and animals of Zebes are seen, but the majority of them are devoid of life, and appear to be in decay.
The Metroid Hatchling, now fully grown, appears and attacks Samus, reducing her energy level to 1. Apparently recognizing her, the hatchling stops, sparing Samus's life.
Samus continues through several more rooms with a natural look before reaching another artificial room. This familiar-looking room houses Mother Brain, the five Zebetite barriers, Rinkas, and turrets, just its predecessor did, but the layout of the room is not identical.
After Mother Brain is defeated once again, her entire pedestal is destroyed, leaving her in an apparent lifeless state. After a short pause, Mother Brain revives, mounting up on a large mechanical body, and resumes attacking Samus.
With the help of the Metroid hatchling, Samus defeats Mother Brain again, and as in the previous encounter, a time bomb is set, forcing Samus to flee. Using the Hyperbeam she acquired from the grown Metroid Hatchling, Samus breaks through a wall in Tourian, revealing its connection to the escape shaft from the original Tourian, and Samus again uses it to reach the surface of Zebes.
The original Tourian is accessible in Super Metroid; located in the lowest parts of Crateria. When Samus first begins the descent into subterranean Zebes, all routes are inaccessible except for a door leading directly downward. This door leads into the escape shaft connected to the original Tourian.
Old Tourian is still in a state of disrepair, with Mother Brain's destroyed holding tank visible. There are no longer turrets or Rinkas, but the room contains several Space Pirates.