The cocoon cavern originally appeared in Metroid, but had a much simpler appearance. It is entirely made of white, square tiles and initially appears as a straight corridor. Firing into the ceiling on the right side (most effectively with the Wave Beam) uncovers a hidden shaft. Samus can jump up the shaft to get to a ledge above the ceiling. A door to a corridor with a Missile Tank is found here, but it can be difficult to get to without the High Jump Boots. It is devoid of any enemies, and it lacks any other purpose than to provide a path through the left of Ridley's Lair.
The room has a much larger role in the remake, but through Sequence Breaking it is possible to skip it. After Samus releases the ensnared Kiru Giru from a room directly above this one, it falls into the floor. This opens the path to Ridley's Lair for Samus, who can then take an elevator into the fortress.
This room is now composed of natural cave rock. The floors appear to be covered in some sort of residue, as when Samus drops down to parts of the floor in Morph Ball form, a noticeable sound is heard, and a cloud of fluid bursts up where she lands. The bottom part of the room now features a rocky outcropping from the ceiling, as well as a Green Hatch blocking access to the next room. Under normal circumstances, this hatch cannot be opened until a short time later. If Super Missiles have been acquired early, Samus can bypass the upper part of the room altogether. Jumping up to the outcropping and proceeding up (after a screen transition) takes Samus to the cavern's upper shaft.
Much of the room here is closed off, including a section just to the left with a door inaccessible from the right side. A single midair block is found here, with three Multiviolas swarming around it. Continuing upward, Samus will reach a dead end, but the Kiru Giru is shown to have burrowed through the floor from Norfair into this shaft. Notably, the color of the rock surrounding the creature is a dull brown whereas the rest of the room has a purplish tint; it may represent decay or sediment exposed by the creature burrowing into the ground.
Samus can then return to the room where she released the Kiru Giru in Norfair and drop down its burrowed hole. By the time Samus reaches the cocoon, the creature has molted from it, leaving its husk behind. She finds it evolved into an Imago in the next room over, and is forced to defeat it. After this, she can exit the hideout through a door that takes her into this cavern's enclosed chamber with the Multiviolas. Samus can fire at an obvious Missile Block in the floor to exit into the rest of the shaft and carry on with her mission.
- Save Room 1 (via Blue Door)
- Imago's hideout (via Blue Door and opening)
- "Kiru Giru's room" (Norfair) (via drop)
- "Hall of pillars" (via Green Hatch)
Inhabitants (Zero Mission)
There are no enemies in this room in Metroid.
- 152 VENTURE TO RIDLEY'S LAIR (page 61)
- "The fallen larva will grant you access to a passage that leads to the right. Run through the passage, take the elevator down to Ridley's Lair and explore. You won't be able to get far without Super Missiles, however. You'll find a larva - the same creature that you freed from the vine - at the bottom of a tunnel on the other side of the wall. Return to Norfair to investigate."
- 153 DROP IN FOR AN ALTERNATE ROUTE TO THE LAIR (pg. 61)
- "After you take the elevator back up to Norfair, run left and return to the place where you freed the larva. You'll find the opening of the larva's tunnel. Drop in, make your way to the left and fall through to Imago's hideout."
- 156 ROCK THE GREEN HATCH (pg. 63)
- "With Super Missiles in hand, run to the right through a gray hatch, then use a standard missile to bust through the floor. You'll drop near a green hatch. Blast it open with a Super Missile."