There is a covered tunnel at the camp used for a tornado shelter. It is 5' wide, with a 1' bench on each side, The lowest beam is about 5'3", with another 6" space or so of heighth between each of them. The passageway is about 30' long.
It's just a nice, cozy place for a brutal, shieldless melee. When the bodies filing in start filling up the entrance, the light is probably going to reduce.
It might be a nice place for a torchlight knife fight as well. 
We may use some electric lights or glowsticks to give enough 'atmosphere'.

It is above ground, and heavy railroad timber construction. We can't hurt it.