Possibly TMI, but I actually figured out the "sex dungeon" thing. Luckily I've got so many more important things on my list of things to do that I'll likely never get around to it. That said...
The house started out basically as a 2br. Enclosed front porch (that has basement under it, interestingly enough). Living room and kitchen on one side, bedrooms down the other. Bathroom out the back, between the bedrooms and the kitchen. I suspect there was originally an outhouse because the bathroom started as a lean-to room, tacked onto the back of the house. Also on the back of the house was almost certainly one of them "Wizard of Oz" storm cellar doors, because there's a flight of steps in the basement that disappear into nothing. More on that later.
But at some point they extended the house out, making the footprint a long rectangle and surrounding the old bathroom. Dining room(?) on one side, undefined entry/mudroom space behind the bathroom, and a weird "I dunno what to do with this space" closet that runs along the other side all the way to the wall of the back bedroom. Then, right down the back side of the bathroom they dug fresh steps to the basement. So as you come in the back door, there's a closet door to your left that goes to a, oh, 12' long, 4' wide closet, and the door to the basement stairs right in front of you. There's only crawlspace under this addition. So about 2/3 of the house has basement and the back 1/3 has crawlspace.
Once we get down in the basement, there's the aforementioned old stairs that led to the old door to the basement and the door to the current stairs. In between is a window hole. So if I get to work with a shovel, I can dig out that corner of the back wall that has a concrete stairwell on one side, while keeping far enough away from any unsupported crawlspace walls, maybe add some bars to the window, and make myself an intimate little sex dungeon worthy of "Silence of the Lambs." Granted, the access is a little undignified since you have to crawl through the opening at the top of the old stairs, but maybe I can put a nice trap door under a rug in the dining room.
And with a basement under the front porch, it would be relatively easy to have a trap door "WELCOME" mat that leads to a basement holding cell. And of course add a secret door to the back of the back bedroom and I have a combination huge walk-in closet, bolt hole escape to the back door. These should all really boost the resale value.