A location in Munch's Oddysee, although not during gameplay; only a cinematic. The Almighty Raisin sends Abe to find it before falling asleep. The Shaman advises Abe to be cautious, due to Magog Cartel forces occupying its proximity due to mineral deposits in the area.
Some time after the first two levels (functioning as tutorials), Abe and crew arrive, apparently having made it past the security forces offscreen, just in time for Vykker's Labs to pass by above (and, thus, Munch). Abe jumps (or rather, is pushed in by Alf), and makes it onto the massive zeppelin before it is too late... only for Munch to collide with him on the way down from the Poop Chute, causing them both to plummet back down to Oddworld, and, miraculously, survive.
The Big Well itself appears to be a form of large geyser or hot springs that shoots whoever is willing to jump into it up into the air (to Vykker's Labs conveniently above it in the case of the cutscene). It is, essentially, the largest known well in the entire series.