Castle on the Falls Sketch

This is from a series of Concept sketches I've been working on, exploring the idea of a castle or perhaps even a town, situated on the cusp of a waterful.
Towns or fortresses that are difficult to get to are particularly interesting to me. Strategic locations can make or break the defense of a castle. Here I am trying to make a fortress or town that would be extremely difficult to attack.

I've also included the process version of this sketch, to better allow my professor to see how I worked this image.

Like many of my sketches, this will ultimately be used as a base for a full-on matte painting.

Photoshop and Wacom tablet.
35-minutes.