CrossBeam
RR: 4.0
This is one of the first two arenas that Adam ever made (Adam the NAB player, that is) - and, as a first map should be, it is pretty simple.  A rectangular room in Asteroid textures, with a "crossbeam" up towards the ceiling, with a wall down the middle.  There are weapons, though the only way to reach the upper area is by respawning there.  Call in the Bots and you can have a frantic few minutes of madness, or if two or three players want a nice simple place to play - then this will do nicely.
   It is a tiny download, so there is really no reason not to add it to your collection!