The Cage

[VictorCharlie]

I prefer the cage...I suppose you could substitue the wire for a clear plastic, but you still have the same basic setup

[donnydarkoIRL]

I think that the shape is essential. The size is also a benefit to some fighters.

But the cage does indeed add a sinister aura to the hostilities.
However, my next option would be a pit, similar to those employed in thailand, but they provide poor visibilty unless the stands overlook them like in the colisseum.