Alright, I have no idea if this has been done or how well it will work, but here it goes.
When humans build castles, they place rock onto land, reaching into the sky. When a normal dwarf builds a castle, he hollows out a mountain and makes it his home. When an elf builds a castle, he decides to be an elf about it and starts singing songs about humping trees and gives up. I, obviously, am none of these. Instead, I have a vision for something far, far, far greater.
Why build up, or hollow out, when you can cut away?
My idea is this: I channel out a great cube, 100 by 100 by 100 Urist in size, with 15 Urist thick walls around it. The top of the castle will be left natural, so that animals can graze and surface booze can be produced. The walls will be home to my military, with enough room for a thousand dwarves (possible hyperbole)! The only entrance will be by a floating walkway through a hole in the walls, lined with fortifications. The world outside the castle will be left barren, channeled to bedrock with not a drop of nature beyond. It shall be impregnable, a masterwork of architecture!
Now, this being my first megaproject and me being a lazy bastard, I intend to build it by creating a shallow fortress, wait until I get a vampire, entomb said vampire such that he shall be forever safe (like it or not) and then just work several dozen waves of migrants to their miserable and untimely deaths.
Now, anyone see any problems with this so far?