Wonderful, looks very organic and pleasing. I know others have been suggesting a (typically) stone keep/castle for defensive works. If you are thinking about adding some, perhaps a more pleasing and fruitful endeavor would be to implement motte and bailey fortifications, or earthen hill fortifications such as the Celtic oppidum or the mounds of Cahokia. These varieties of earthworks would fit particularly well with the graphic design and goal of this generator.