Very much like how you did the chasm effect. I will have to work on replicating that. The land 'blobs' of rock seems fairly straight forward and cool. Did you draw in the crenelations by hand or was there some cool short cut? I like the detail of the placed stone along the walls and tower elements. Sketched in on your tablet and set to a low opacity?

Overall I like the design. It suggests that someone was just building into the terrain rather than trying to terraform it to fit their design for a castle.

Awesome job.
-GP