It's quite remarkable they managed to fit a weird arena like that within the hull of a cruise ship. However, it also explains something about the boring shape the ship had, to have room for that place. I'd suppose it claims the whole aft portion of the ship. It can't be in the middle as there'd be little space to get past it.
Shipyard anywhere else in the world: "Are you quite sure you want to waste... use all this space for the strange arena?"
Shipyard in China: "It makes perfect sense to have a needlessly huge and complex martial arts arena aboard! A most brilliant ship design!"