Travel: Microwaves for mermaids: The world's first underwater hotel is in a lagoon at Key Largo. Sue Nelson dived in

THERE are hundreds of motels listed in Key Largo's equivalent of Yellow Pages, but only one under the heading 'Motels, Undersea'. It is an eye-catching entry and deservedly so, because the Jules Undersea Lodge is the world's first and only underwater hotel.

The Lodge is part of Key Largo's Undersea Park, a man-made tropical lagoon where visitors can snorkel, scuba or watch educational films in the Aquarium Theatre. It is easy enough to find; just look for mile marker 103.2 on the island's sole highway, the US 1, which threads together 31 islands in the Florida Keys. The main attraction cannot be seen, of course, but bubbles on the lagoon's surface hint at what lies below.

There, 30 ft down among the angelfish, I passed the remains of a Spanish galleon and turned right at some 17th-century cannon. Red snapper and barracuda ribboned through arches of coral reef but a shoal of mud-striped grouper had other ideas, clustering above a huge box-like structure encrusted with seaweed and barnacles. Funnels, almost obscured by fish, protruded from its flat roof while the ends of the 'building' sloped anvil-fashion towards the lagoon floor.

This was Jules Undersea Lodge. As we felt our way along the hotel's algae-clad wall, a large porthole appeared out of the gloom. Inside, a woman rapidly covered herself with a bathrobe and grinned at her Peeping Toms. The instructor, John Dotten, then signalled for me to duck, though I could not understand why. Then I saw the structure's four supporting legs; we were about to enter the hotel from beneath its floor.

A moment later we surfaced in the wet room's 'moon pool', ditched our scuba mouthpieces and breathed air that was surprisingly fresh. The wet room is the sole access point into the Lodge, the underwater equivalent of a reception desk - but without the ambience. It is simply a functional changing room of cold studded steel with a ceramic tiled floor. A sign hung from one of its bare walls: 'Welcome to the Five Fathom Club'.

Thirty feet under the sea is hardly the 20,000 leagues imagined by the Lodge's namesake, Jules Verne, but it was enough for me. Suddenly I felt tired, cold and grateful to be able to breathe unaided. 'You'll feel better after a hot shower,' John said, helping to remove my tank. 'And then you can make yourself a cup of coffee.'

Showering, apart from restoring body warmth, removes salt water and prevents corrosion in other parts of the Lodge. Dress code is strictly informal, mainly because luggage is restricted to an overnight bag which is delivered inside a waterproof canister by instructors.

'Hi there]'

Carla Rush, modesty recovered, introduced herself as the Lodge's operations director. 'I've just been sorting out the towels and making sure the lodge is clean,' she said. 'Have you had a guided tour yet?'

Wearing swimsuits and bath towels, we climbed through one of two circular doors on either side of the wet room. I found myself in a customised cylinder, carpeted all over to deaden any echo and with a giant porthole at one end. A luminous glow emanated from the lagoon and bathed us in a sap-green light. Fish nibbled the window, gazed at their new neighbour and sauntered out of sight.

'This is the living area,' Carla announced as I stared dumbfounded at the amount of mod cons in this underwater tin can: mini-kitchen, microwave, stereo, CD player, TV, video and a selection of films including Splash], The Abyss and The Creature from the Black Lagoon. 'I think there's a Jaws movie too,' John said with a grin.

A selection of fizzy drinks stood among the fruit juices in the fridge. 'You'll find that carbonated drinks go flat really fast down here, because of the increased pressure of the compressed air,' said John. He was right. I sat at one of the mermaid-shaped tables, released a ring-pull and gulped. The bubbles tasted ten minutes old and decidedly tired. A sachet of microwaveable coffee fared better, despite being alcohol-free due to Lodge regulations. There was just one thing missing: food.

'No problem,' said John. 'Just make a choice from the menu; it's then prepared topside and brought to the Lodge for guests to complete in the microwave.' I glanced at the dishes on offer: filet mignon, lemon chicken . . . 'If that's too much of an effort, there's always a mer-chef service for an additional fee,' he added.

We climbed back through the circular doorway, crossed the wet room and entered the other 'wing' of the hotel. 'The two living quarters are identical in size,' Carla informed us, 'both 20ft in length, 8ft in diameter and connected by the wet room.' Does anyone ever get claustrophobic?, I asked. 'No,' she replied without irony, 'it's too large for that.'

The Lodge is best described as a cross between a spacious mobile home and a couchette. Bunks in the bedroom cylinder sleep a maximum of six and, according to John, it works best with just two couples. 'Otherwise you have to be good friends,' he said, laughing.

Everything is decidedly compact. The novelty, of course, is due to its location and because it genuinely offers a room with a view. There are 40 in-diameter portholes at both ends of the bedroom, so this is the the best place to relax.

John pointed out that things had not always been this comfortable. 'It used to be filled with electronics equipment, and everywhere was as basic as the wet room.'

Jules Lodge was originally a research laboratory named La Chalupa, Carla explained. 'It was operated about 10 miles offshore from Puerto Rico until the mid-Seventies, when funding for ocean research became tight.' The lab was then taken to dry-dock in Miami until Ian Koblick, its co-developer and owner, decided to convert and operate it on a commercial basis. In 1987 the Jules Undersea Lodge was ready for business.

The research continues, however. Last year, for example, the hotel provided Nasa with an ideal location for psychological isolation tests on astronauts. 'One man stayed down here for 69 days and broke the world record,' she said. 'When he surfaced the first thing he noticed was colour - sunlight, the bright greens of trees and the vivid blues or reds of people's clothes.'

In the sap-green gloom, I could understand exactly how he felt. But getting used to the submarine atmosphere is by no means the only challenge for guests. First of all, there is the training. After satisfactory completion of a medical history questionnaire, you must take a four-hour resort course at the Lodge, which allows you to dive to the hotel. Non-divers like myself are taught the safety and equipment basics, and then gradually introduced to the depths of the lagoon.

But the major problem with staying in the world's only underwater hotel is not the course, but the cost. The cheapest rate is dollars 250 ( pounds 174) per night per person for six sharing and, if you are only resort-certified, any further dives must be accompanied by an instructor for dollars 25-dollars 40 per hour. This scuppered my budget, but did not deter a party of four chiropodists from New York and California.

Brett DeCesare had read about the underwater hotel in Sports Illustrated. The morning after their overnight stay, he spoke to me from the Lodge via an intercom phone. 'There's much more than I expected,' he admitted. 'I did a fibre-optic trail night dive and afterwards we ate lobster and watched The Little Mermaid. It's great] All sorts of fish come up and watch you eat.'

Jules Undersea Lodge is on the US1 highway, a one-hour drive from Miami International Airport. For reservations call or write to Key Largo Undersea Park, PO Box 3330, Key Largo, Florida 33037. Tel 010 1 305 4512353. Rates are dollars 250 ( pounds 174) per person for a group of six; dollars 295 for double occupancy suite and dollars 1,500 for exclusive use of Lodge. A one-day resort course diving certificate costs dollars 125.

(Photograph omitted)