As my plane loops down towards Cuba, the vivid turquoise waters contrast with the dark reef that rings the island, stretching endlessly into the deep. In my mind I am already there, savouring the ever-magical moment when the surface of the sea recedes overhead and I first glimpse the hidden world below.

Having developed a serious diving addiction on my travels, I am rubbing my hands in glee at the prospect of Cuba's bountiful Caribbean seas, reputed to be among the world's diving hotspots. With crystalline waters, balmy sea temperatures and as yet relatively untouched by mass tourism, Cuba is home to an astonishing array of sealife including sharks (from whale to tiger), rays, turtles and pristine corals. I have one month and 3700 kilometres of coastline to explore - sites include the Bay of Pigs, the northern cays immortalised in Ernest Hemingway's novel Islands in the Stream and even the ill-famed Guantanamo Bay. It is a veritable dive safari.

My first stop is the Bay of Pigs, more widely known for the 1961 US invasion than for its underwater offerings. It is not reputed to be one of the country’s best sites, but it is close to my arrival point in Havana and I am keen to get in the water. Thinking I will save my time – and my cash – for the most renowned locations, I cautiously book one initial dive. But once I have glimpsed the outstanding quality of the coral and the plethora of aquatic life, I am hooked, and soon sign up for three more.

The bay has over 20 dive sites, with gigantic underwater canyons and caves and atmospheric wrecks looming out of the reef. On my first dive I see several large barracuda, groupers, crabs and lobsters, but it is the condition of the coral that is most impressive - an astonishing variety of species in all but immaculate condition. The visibility is up to 25 metres, meaning that even at depths of around 30 metres the colours are still vibrant, with large purple gorgonnese fans particularly striking.

The seascape is astonishingly varied and intricate - on subsequent dives, we explore seemingly endless canyons, caves and tunnels, and along giddy coral drop-offs looking out to the big blue. We encounter moray eels, yellow stingrays, giant pufferfish, the quirky horned cowfish and blindfish – a fascinating species which see only light and dark; brandishing our torches in a cave soon attracts a large swarm.

Dives here are among the cheapest in Cuba, £15 per dive including equipment, with discounts for multiple dives. I dive with the Octopus Club attached to the Hotel Playa Larga at Playa Larga, and dive groups are small, (I never dive with more than one other person plus the guide on all four dives.) The guide, Pepe, is professional and helpful, and the standard of equipment as good as any in Central America. With an advanced open water qualification, most of my dives run to around 30 metres, though the instructors will happily cater for less experienced and qualified divers, even absolute beginners.

But it is not open water dives for which the Bay of Pigs is most famous. The Peninsula de Zapata, in which the Bay sits, is dotted with flooded tectonic caves or cenotes, similar to those which delight tourists in Mexico. One of the most popular, Cueva de los Pesces, has an underwater tunnel system which leads out to the sea, allowing tropical fish to populate the cave. An astoundingly beautiful and secluded spot, the cave is perfect for both diving and swimming, and indeed, the latter is as far as I get - after having arranged to do my first ever cave dive here, I chicken out at the last minute, deciding I am not sufficiently experienced to brave the dark narrow tunnels in which panicking can mean fatal injury. However for those with the experience and the courage, these cenotes are renowned far and wide for the diving opportunities they offer.

Following four dives to rival anything I have experienced in the Red Sea I head off to my next stop, the picturesque Cayo Guillermo off the northern coast. This small island is connected, like neighbouring Cayo Coco and Cayo Romano, to the mainland by a 29 km causeway, itself a stunning drive across shallow turquoise waters dotted with flamingo colonies and lush mangroves. Hemingway spent much time in the northern cays and for good reason, since the icing-sugar beaches here are amongst the most beautiful in Cuba, truly living up to the Caribbean idyll.

The only places to stay here are all-inclusive resorts but are good value at around £35-£52 per room per night, including all food and drink (Hotel Sol Club Cayo Guillermo, four-star.) All the resorts have their own dive centres - I use the Hotel Sol Melia Cayo Guillermo, where dives are around £25 for the first dive with discounts on all subsequent dives. Equipment, however is extra. Unlike the Bay of Pigs, where most dives are done from the shore, the 20 or so dive sites here (along with more on longer excursions) are generally accessed by boat. Again, groups are small, with just two to four divers when I visit.

I limit my dives here to two as the visibility on the north coast at this time of year is not optimal, approximately 15 metres. However we see some beautiful coral pinnacles and wrecks on our two drift dives, and, most thrillingly, we are treated on our second to encounters with nurse sharks and an immense stingray approximately two metres in wingspan and three metres in length. The sight of this giant gliding gracefully above us, its wings flapping slowly as if born on a buoyant breeze, inspires a deep sense of awe at the magnificence of nature’s handiwork.

Deciding where to go next I am spoilt for choice - Cuba has almost 20 major diving zones on both its Caribbean and Atlantic coastlines, each with a choice of sites to satisfy even the most prolific diver. You could dive here every day for years and never visit the same location twice.

Santa Lucia in Camaguey province is perhaps one of the best spots to see bull sharks up close, while the Isla de la Juventud and Varadero are both lauded for their world-class opportunities. More remote, but consequently pristine, is the archipelago known as the Jardines de la Reina, sometimes described as the Galapagos of the Caribbean. Accessible only on live-aboard trips or from the floating hotel La Tortuga, this uninhabited chain of islands forms part of the longest barrier reef in the Caribbean, and is home to numerous types of shark as well as the largest populations of hawksbill and loggerhead turtles in the Caribbean.

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