this is more or less what I meant for mm2dw1
Red = caves
yellow = ground and slightly below
green = above ground
blue = second floor
purple = third floor
magenta = highest walls

EDIT:
I don't want to redo all that, but on second thought it would probably be better to just get rid of the catwalks and the little ladder niches in the corners of the balcony and instead just make it a deeper tunnel on each side that goes into a spiraling staircase to the corner of the balcony. That way you can get rid of the ladders inside all the bunkers and make the roofs of those only item-accessible again while maintaining the distinct open arena + outer ring idea I explained earlier.