Let's be honest: most hotel rooms are just variations of the same beige box. But if you're the kind of traveler who thinks a standard king-sized bed is a missed opportunity for adventure, we have some delightfully riveting options. From sleeping 21 feet underwater to hunkering down in a man-made cave 70 feet below the desert floor, here are the 10 craziest, most eccentric hotels in the U.S.