Named for "20,000 Leagues Under the Sea" author Jules Verne, the Lodge is one of just two open-for-business hotels on this list.
It was originally built in the 1970s as a "mobile undersea habitat," but it was converted to a hotel in the 1980s. The the no-frills digs are really aimed at scuba-ers who relish the ability to easily slip out for a dive.
"When guests visit Jules' Undersea Lodge in Key Largo, Florida, they discover that the name is no marketing gimmick," the hotel's site reads. "Just to enter the Lodge, one must actually scuba dive 21 feet beneath the surface of the sea."
Per-night rates range from $675 per person for single occupancy to $300 a pop for larger groups. Jules even offers underwater weddings.