It takes place on some kind of flying fortress in the clouds that consists mostly of rails, some riddled with spikes. It features things like Hang Gliders, parachutes, and rocket boards. It is also the first of two levels with non-bottomless pits (the second being Dead Line). These are actually big, horizontal laser beams at the bottom of some falls that the player must avoid because touching them causes instant death like actually falling into a bottomless pit. There are also some 3D areas where the player flies around in a Hang Glider and dodge enemies. The song for Altitude Limit is "Get Edgy".
The boss is the Egg Eagle. It is fought on a high metal platform on top of the clouds and tries to destroy the player by jumping on them or crushing them with its beak. It will even try to blow the player off of the platform by using its wings as a giant fan. The cyan Chaos Emerald and clear Sol Emerald are found here.