So, Syvarris, Krom and I set out yesterday to make a castle completely in the Nether. We started in what used to be my entrance into the main Nether, but we mined it out, flattened all the walls, and lit it up to make it look like an outpost.

Here are the initial results with Dusk helping me:
Project NetherKeep-2011-06-15_14-35-59-jpg