This map had only limited release; a slightly revised version was issued later by Skippy as Crossfire. If you check the review for that, you will see a screenshot from ground level, looking up; here, through the magic of cheat codes, we have a screenshot taken from the top, looking down!
Really, this map has never been finished, which is a shame, because as well as the useful ground-level battleground, there is a lot more (potentially) here. The below-ground level, which you get to via the descent of the grey oval you can see in the middle of the main open area, is fine - all it needs is a way out afterwards, an elevator or a teleporter or two. And once you get through a door in the wall (visible in this shot as a lighter grey square), you have an elevator up to the "clubhouse" level that we are floating alongside, where the nerfcannon is. And from there, a swooping "magic carpet" takes you on a wonderful ride down to the ground again! The only problem is, that grey door in the wall has never been made to open, so unless you "ghost" through, and then change to "walk" again, it is all hidden and unattainable...
Sometimes maps just cannot be put right if they go slightly wrong, and any attempt to fix them just makes the whole structure fall apart. I suppose that is what has happened here for Skippy, but it seems an awful shame, as even the partial versions have been popular - the fully finished arena would have been excellent.