Ubiquitous and I just made this file to test all weapons for the chuck's decreasing life. There are 527 weapons and items in the arena and under it. Pretty much all weapons in the game including NPC's weapons.
Warning: The NPC weapons you should avoid. some of these unusual weapons will make the game crash if picked up, some you can't drop. So I suggest avoid the weapons you are not familiar with.
Soon I will make a mod for this, with doors out of the arena. This will be a sort of weapons depot before traveling outside. All 527 weapons are dispensers.
Reaching the room
You can only reach this room two ways, 1. modifying missions.txt, which i didn't do here, or 2. if you have debug mode, which you do ubiquitous, in your users.ini or masters.ini add
then start game in debug mode. DEBUG ENTER on main screen.
No infinity mode changes in this datafile.big
This datafile.big is completely untouched except for the changes in arena (gs_biketutorial.txt).
Weapons under the floor
The last 107 weapons, mostly guns and pushable items, is directly below the arena's middle. in debug mode, use F2 and float down there.