The Aquatic Mine is an abandoned mine located within the vicinity of Pumpkin Hill. Knuckles discovers this place in his search for Master Emerald shards. In keeping with the imagery developed in his previous stage, many of the symbols found about the mine seem very Halloween themed. This level is also absolutely infested with Boos, enough to the point that a warning sign has been posted. It appears that at some point during its operation, the mine flooded. There are three switches present in the level that affect the height of the water within the mine, adjustment being necessary to reach the higher levels of the forlorn place. There is an optional upgrade available for Knuckles in this level, the Air Necklace. Consider it an infinite oxygen tank that allows Knuckles to stay submerged for any period of time without having to resurface for breath. When returning to this level to complete further missions/goals, this upgrade is very helpful.
- There is apparently a connection between the Aquatic Mine and the sewers of Central City, as Knuckles emerges from a manhole in his next cut-scene, simply stating to his shocked friends that he had "gotten lost in the mines."
- The 2P stage Pool Quest is part of this level.