I believe it is just a superficial 'ruined castle'
Thing is, it uses exactly the same tile as an actual map feature. I forget which one now, but my first game in beta 2B had the two of them just a few tiles away from each other, and it was enormously confusing. Tbh, this is just one more symptom of an endemic problem: namely that proper interactable map features are entirely indistinguishable from eye candy and random fluff pieces, because they all use the same art style, and even component models.
Elemental's art style means that everything is outlined with those thick borders. But that practically screams that the item in question is something set apart from the background, and therefore usable. Which is exactly what these background eye candy pieces (not just this ruined fort, but even the little rock outcroppings have this) should not be doing.
Compare to Civ4. You'd never mistake a goody hut or resource for a bit of background nothing. Mostly because Civ4's background eye candy, such as it is, makes sure to stay well in the background. And yet Civ4's maps look significantly less bland than Elemental's do.
