Floating Island & Floating Island 2
From Sharpknux, a map a bit similar to his own Volcano, but rather more complex. A nice grassy area surrounded by a skybox, with a South American style pyramid in the middle; grab the jumping sneakers and you can hop from there to tops of pillars with a shield and a megapower, among other things. Various rocks and pillars provide cover, there are weapons around - a pleasant if unambitious place to exercise your triple strike.
But wait - there's more. Fall through one patch of grass into a channel that leads to a cave, with useful pick-ups; an elevator allows you to return to the surface. And leap down the central well, and you reach a lower ocean. Try to avoid landing on the small raft moored directly below, though, or you will kill yourself! When trying to board the raft, try to avoid swimming underneath it, as what is called the "giant squid glitch" will grab you and prevent you getting up to the surface until your health has run out! Jumping off the edges of the top area will also get you down into this ocean. As well as a pair of power-ups, the raft houses an (invisible) bounce-pad; leap onto it just right, and you can bounce all the way back up to the cave. I haven't actually managed that, but Sharpknux assures me it is possible, if you look up during the jump!
So, definite possibilities for fun, and also a good map for going the "adminlogin" route, and flying around, though I think FeEdiKo was taking things to extremes, spawning a chain of doublers and points-targets in the sky!
The version 2 was designed to get rid of the "giant squid" and "can't bounce up" problems. For me it did the former okay, though another player said he did get caught; I still couldn't bounce all the way up from the raft, though, however many times I tried.