If you're in need of a dungeon, but can't afford the frankly exorbitant prices that dungeon builders charge these days, you can make a virtue of necessity and build your own dungeon. If you don't have the good fortune to live in a medieval castle, a suburban basement will have to do.
Clean everything out of your basement that will ruin the dungeon ambience that every prisoner expects. Ping-pong tables, hockey equipment, canned goods, and old Milli Vanilli posters will have to find somewhere else to go.
Build interior walls out of large limestone blocks and mortar. Reroute a bit of water from outside so that it begins to seep down the interior walls, creating dampness and mildew.
Release the bats, rats, spiders and snakes into the dungeon and allow them to breed at will.
Direct the spiders to the corners so that they can begin developing impressive cobwebs.
Cover any windows with iron bars, preferably rusty ones that clank satisfyingly when they are hit. Use vertical bars or iron grids.
Chain instruments of torture to the floors using iron rings. A rack is a nice touch if you can get one.
Attach more iron rings and chains to the walls for hanging things and people. Be sure to include one of those iron ball things with spikes sticking out of it, attached to a big oak stick by a chain. No dungeon is complete without one.
Litter the floor with bones and half chewed bits of offal. Put a rat-chewed straw mattress in the corner, preferably where the foul water is dripping down the wall.
Affix torches to the walls. Be sure that you put them far enough down the walls so that they can flare, sputter, and create choking smoke without setting your house on fire.
Build a hidden entrance to your dungeon by putting a trap door into your first floor and putting a rug over it. Affix the trap door with enormous iron hinges that screech menacingly whenever the trap door is opened. Be sure that they screech; if they don't, the dungeon won't work.
Remove the door that went to the basement before you turned it into a dungeon and drywall over the door space so that the only access to the dungeon is through the trap door.
Grow attractive shrubs around your basement windows to obscure the iron bars.