Some adrenaline hounds aren't content just to climb the sheer sides of cliffs. They like to camp on them, too ... and we don't mean just pitching a tent at the edge. Rather, these intrepid cliff dwellers enjoy affixing tents or sleeping platforms over the sheer sides of cliffs (with nothing underneath except air and, of course, the rocky bottom far below) for what must surely be some electrifying shut-eye. Talk about active dreaming. Sleeping on the edge isn't for everyone, but at least one cliff-hanging daredevil has found a way to capitalize on his precipitous passion by using it to raise money for charity.