I'm missing one area in the Monster Arena, but I have no idea what it could be. It looks like this:

Besaid --- Kilika
Mi'ihen Highroad --- Mushroom Rock Road
Djose Road --- Thunder Plains
Macalania --- Bikanel
Calm Lands --- Sunken Cave
Mt Gagazet --- [unknown]
Omega Dungeon --- Area Conquest
Species Conquest --- Original


So the question is.... Can you name the unknown?
....please?