A special room hidden away, usually in a basement or underground with sound proof walls, suitable for deviant sexual activity, or surprise sex, with unwitting hitchhikers, prostitutes, strippers, or other partners.
Steve - "Hey Bill, did you hear what Josiah and his dad built last weekend?"
Bill - "Yeah, man, that's cool... I can't wait to get my sister in that rape dungeon for a little surprise hey-nanny-nanny. I be knockin that bitches bottom out. Dey rapin' e'rbody down dere!"