The Planet Ocean Underwater Hotel, in Key West, Florida, has just been granted a United States patent for its modular undersea accommodation design. Although the project is still in the planning stages, a prototype is reported to be under construction.

The artist's impression of the completed hotel (above) looks similar to the Poseidon Undersea Resort (below), which was originally expected to open in 2006. A Poseidon website still tempts interested parties with the promise of "the culmination of every elite vacationer's vision", although neither opening dates nor exact location (somewhere in Fiji) are confirmed and its Facebook page hasn't been updated in almost two years. Another undersea project that's apparently dead in the water is Hydropolis, a subaquatic hotel that was announced with much fanfare in 2003 and expected to open off the coast of Dubai in 2006. Its former website no longer exists.

All three projects seem obviously worthy of a Jules Verne novel, and it's interesting to note that the one underwater tourist property that is actually operating was named after the futuristic French novelist. Opened in 1986, the modestly sized Jules' Undersea Lodge, in the Florida Keys, offers two self-contained rooms about six metres below the surface, to which guests must scuba-dive. A chef can be sent down to prepare meals, or you can have pizza delivered to your door. Overnight rates start from US$800 per couple.

Planet Ocean Underwater Hotels are optimistically planned for Egypt, Malaysia, Hawaii and the Bahamas but, if past efforts are anything to go by, don't hold your breath.