One way to draw a simple castle is to draw a horizon line, add two rectangles in perspective and draw guidelines for any towers and the main building. Next, draw darker lines to define the main structure and add extra details or color.
When drawing guidelines for the castle towers, draw them with a cylindrical shape. Remember to keep the guidelines light since some of them are colored over. Next, add defined cuts for the ridges on top of the towers. Draw in additional details for a gate, windows and any other desired accents. After the dark lines for the building outline are filled in, darken the defining lines for the windows, bridge and doorway.
The next part is to fill in the castle with colors and shading. The windows and darker parts of the castles should be shaded in dark colors. To finish the drawing, add background details such as a sky, mountains and water around the bridge that enters into the castle.
These instructions are suited for a castle on a flat landscape. To draw a castle on a hill, use the same basic shapes, but create the horizon line by drawing two perspective lines that cross each other at a slight angle.