Two point perspective is the method of creating two vanishing points, in this case a medieval castle
Process is to create a horizon with two multiple point stars on each end, which are the Vanishing Points
Circle area represents the drawable area where it is most accurate. It's mainly for 2D artworks but it also works well as a starting point for 3D level design.
The blue lines from the vanishing points mark where parts of the image would enlarge and get smaller depending on the perspective.