I wanted to create a defensible castle, but I had no idea what it would be defending. I just had this image in my head of a wall jutting out from the mountainside, so I started drawing a rough outline with some notes about what the different rooms were. I focused a lot more on the names of who would be living there than I did on what to call the place, or the reasons for its existence.
Beyond that, I haven't really detailed it. I'm thinking of redrawing it and putting a town around the outside wall.