Well, xpian challenged me to do something waaaaaay out of my comfort zone. I don't have a WIP yet, but I wanted to at least get the thread up so it'll be harder for me to back out.
Here's his brief:
1) A great castle was built long ago by an other-worldly host and set in the clouds to dominate the lands below.
2) During a cataclysm of angelic/demonic warfare, the castle was damaged and crippled, but not destroyed.
3) The magic anchoring the castle to the cloud held, the stabilization didn't, and this made the castle flip over. Now, instead of the castle pointing up at the sky, the towers and ramparts point toward the earth, a forest of stony spikes sticking down out of the bottom of the cloud.
4) The nearly divine magic used in the castle's construction meant that it didn't just fall apart and plummet to the ground 4,000 feet below. It remained hanging in the sky as a cracked and shaken husk of its former glory. Where once its battlements had known only sunshine, now they were eternally shrouded in shadow, mist, and drizzling rain.
5) For centuries the castle was like a Flying Dutchman, an apparition seen from the ground as a bad omen drifting past overhead.
6) Now the castle has been discovered. A dragon has taken up residence in the tallest towers, which are now the ones closest to the ground. The dragon's servants have built up and repaired much of castle in its inverted state, and have converted it to the thing the dragon desires most: a mobile base for piracy. The dragon's sky ships venture forth, sometimes accompanied by the beast himself, and raid towns, rich houses, and shipping, bringing the treasure back to the dragon's lair.
7) The one place the dragon and his servants have learned not to go is the catacombs and dungeons -- the parts of the castle that are now highest in altitude and always buried deep within the mists of the cloud. Here is where the true source of the castle's enduring magic is to be found: a Death Tyrant. This undead beholder was once a part of the original faction that made the castle, centuries ago, and its indomitable will is what keeps the castle floating still. The catacombs are filled with the undead things that it has created over the years.
So! Create a map of this inverted cloud castle. I call it The Seething Harrow. Perhaps you want to make it isometric and show just a few important levels here and there. Perhaps you want to make it top-down with a side-view sketch. You can choose your medium and mode.
9) Ideally there should be some catacomb/dungeon depiction where the undead beholder and his slaves lurk, some middle ground no-man's-land level(s), and some tower levels where the dragon and his sky ship pirates reside. There should be a chamber big enough for good sized sky ships to pull into.
10) Here's a possible sample map of something similar, although this is obviously right-side-up and fairly lumpy. http://dc402.4shared.com/doc/1--qvpTZ/preview002.png