UNC - Training Arena
I assume we are in CurtSquirt territory here, and a pretty different sort of map this is - as you can see from the eight pictures above! You arrive in the "Training Room" (top left), and once you get rid of any lurking Bot, you choose any of the doorways - some on one side of the room, and some opposite. Each cubicle equips you with the weapon shown above it, and you are teleported into another room, where a similarly-equipped Bot player is waiting. And you fight - if you lose, back you go, and if you win, you need to go back through the suitably-untextured door.
As you can see, there are various rooms, in the different NAB textures; I may have missed one or two, but you get the idea! The Luna place was tiny, and the player seemed to have gone off for a tea break; it seems that the Bot players do occasionally wander through the doorways into each other's territory, as I occasionally noticed reports of action in rooms I wasn't in!
As a training arena, this seems an excellent idea. No trophy room or clubhouse for UNC, the Ultimate Nerf Clan, just a place to keep your skills fresh. Unless you can persuade Curt or Mike that you are an especially deserving case, I imagine you have to actually join their clan to be allowed access to this map, which may be a slight drawback...but it's nicely set up, certainly.