I think it's shaping up quite nicely! What I would recommend for detailing is this: Try to tell a story about what has happened since being abandoned, for instance, take an abandoned building and there is some rubble on the ground. Why is that? Because if you look up, you can see the ceiling has been partially destroyed by a beam that fell down at some point. Things like that can make it much more interesting to look at Also, try to think about the conditions of were it's located at too. Think about an abandoned car, if you have it in a map set in a desert, it will be very well preserved because of the dry climate. Now put it in a map set by a coast, the car will be in much worse condition because of the moisture in the air. Lastly, for an abandoned castle, it looks oddly intact as if it were still maintained but just with lots of plants try to make it more dynamic with cracks, holes, or even partially destroyed buildings!