3. Jules Undersea Lodge, Florida, USA
Only certified divers are able to visit this submerged Key Largo accommodation as the only way in is 21ft under the sea. It was built as underwater research lab in the 1970s but is now a novelty submarine habitat hotel that appeals to scuba fanatics looking to spend a unique night in the deep. Food is prepared by a mer-chef (how’s that for a job title?) and unlimited dive tanks are provided so you can explore the reef around your bed.