In Sonic The Hedgehog, some levels wrapped around from top to bottom. Some levels also have water in them. What confuses me is that a few levels have both. The bottom wraps around to the top, so the notions of up and down become relative, yet part of the map is underwater.
For a good example of such a zone, consider Labyrinth Zone 3 from Sonic 1, which features both an infinite water slide at the beginning and an upward-climbing rising-water chase-scene doom gauntlet boss fight at the end, in which the water rises up about 1.5 times the actual height of the map.
Can anyone explain how they made this work? Is there a "bottom" to the underwater area somewhere, cleverly manipulated so that it is never visible on screen? Or is there something more interesting going on?