It looks just like leftover remnants of a castle..however if you look at the little images in the boxes you can see that it forms a perfect compass -- a navigational instrument~. North, south, east, west on the orange outer ring and northeast, southeast, northwest, southwest on the green middle ring. Of course this might not be true in game, but picture wise it looks like a compass.
Design wise, it almost looks like the castle was built to withstand a
flood sixth umbral era, seeing as the legs prop it up and off the ground. But of course look at all the water, but we don't know if that's from Bahamut or not. But looking at the map, there's a HUGE area in the middle where this place could have existed.