A mechanical hatch exists in the maintenance area below the Aurora Chamber on SkyTown, Elysia. It is locked in gameplay, and cannot be opened by Samus, nor can it be destroyed with her weapons fire. Where it leads to is unknown.
The hatch appears to be comprised of three metal gates shaped like an octagon, with an ornate cross-shaped design in the middle. The center of the "cross", and each point contain an open hole; these split apart when the door opens.
Shortly after Samus vaccinates Aurora Unit 217, curing it of the corruption virus, Ghor appears. He damages the room's circuit boards and leaves through the mechanical hatch after being shot by Samus. Ghor is seemingly able to open the hatch by snapping his finger. Because it locks behind him, Samus is not able to pursue Ghor, but she later confronts him at the Main Docking Bay and mortally wounds him.
"Mechanical hatch is locked. There doesn't appear to be any way to open this door."