How to decorate your dungeon

1. Get a rack. Even if you never use it, a rack is get for inspiring a foreboding mood in your captives.
2. Have a bunch of chains. Thin ones, thick heavy ones, and don't forget some with rust! The best thing about chains is that you can have a few guard moan and rattle them at midnight so people will think the dungeon is haunted.
3. Bones. Since most of your captives will likely be uneducated peasants, just scatter some animals bones on the floor. Add to that a skeleton slumped in the corner of one cell, and you're well on the way to a grim atmosphere.
4. Train some rats to hassle your captives. It'll be hard to sleep with the scrabbling of tiny feet steadily getting closer to you.
5. Don't forget to install some leaks. A dank dungeon is a miserable dungeon.
6. Keep it cold. That rough stone floor should sap the warmth right out of your captives.
7. Don't worry about stains. Someone spill their tomato soup? Just spread it around and let the imaginations of those who see it run wild.
8. Forget the bright lights. A dim dungeon is more likely to cause your captives sorrow then a well lit one. Plus, the dark has a way of making even the most mundane objects appear menacing.
9. Hire professional prisoners. Keeping a least one cell full at all times is great for those unexpected inspections. And remember: you don't have to pay the actors until you release them.
10. Have a variety of holding cells. Some with iron bars, others that are just a covered pit, and some with frightening metal doors. By having more then one way to imprison your captives, you can customize their experience to their individual fears.