9 natural underground swimming pools

Dive deeper than ever before, to subterranean worlds and kaleidoscopic grottos at these natural underground swimming pools.

At first glance, it’s hard to believe that the Blue Cave in Kastellorizo is a natural phenomenon. The way the sunlight reflects off the turquoise sea water, bathing the entire cave in blue light, looks a little otherworldly but it’s all real. Better yet, this Greek island is just as beautiful above ground as it is below, so grab yourself a room with a spectacular view at the harbour-side Megisti Hotel.

Thousands of years ago the dome of an underground river collapsed and created one of the USA’s most idyllic swimming holes. A free-flowing waterfall tumbles into Hamilton Pool, while the remains of the rocky roof provide swimmers with respite from the Texan sun. Limestone slabs around the water edge, in the meantime, are perfectly placed for an impromptu picnic. Looking for somewhere to stay? The homey Sonesta Bee Cave Austin is just 25-minutes drive away.

Maya tradition used to have it that the naturally-occurring Yucatán cenotes granted humans entrance to the afterlife. Today, these underground pools are popular among travellers eager to swim in the sapphire, sunkissed water and admire the cathedral-like ceilings – an awe-inspiring experience whatever your beliefs. Dry off at the nearby La Casa del Angel and then drive over to the archaeological site Chichen Itza for further insights into the Maya people.

A 19th-century Tuscan villa converted into a luxury spa hotel, Grotta Giusti was built on top of a natural hot spring and cave network. While above ground, all the traditional facilities one might expect at a four-star hotel are available (a sizeable pool, a lavish restaurant, etc.), below ground, there’s a little more to surprise you. The caves are part spa, part divers' playground, so lounge in the candle-lit steam room, or don a wetsuit and dare yourself to go cave-diving. And while you’re in Tuscany, why not discover Florence, the heart of Renaissance?

You can visit the atmospheric Poço Azul every day of the year as this underground swimming hole maintains an average temperature of 23°. The time you visit is, however, very important. In the early morning and late night, the sunlight filtering through the rock makes the water so crystal-clear that swimmers look like they’re floating 60 feet in the air. To give yourself the best chance of capturing this optical illusion, stay nearby at the Hostel das Estrelas.

Another underground swimming spot that has to be seen to be believed, the Playa del Amor sits deep within the verdant Marietas Islands. This ‘Hidden Beach’ or ‘Lovers Beach’ can be reached by taking a long water tunnel, leading from the sea. Its white sand banks make it a relaxing spot to spend an afternoon. Travellers in search of a slightly more traditional retreat will love the Xiobella Boutique Hotel - Punta de Mita, with its outdoor swimming pool and sea view.

The Green Cave entrance opens directly onto the Adriatic Sea and adrenalin-craving travellers often opt to hike up the soaring cliffs and then leap into the waters below. From there, you can swim into the cave or opt for a leisurely boat ride. Inside the cave, sunlight reflects off sea-algae to transform the water from sapphire to emerald. If you’re looking to stay overnight in the area and mix with the locals, the Barba Ante guest house on the nearby island of Vis is recommended.

A moment of Mediterranean-style escapism on Ontario’s striking shoreline, The Grotto in Bruce Peninsula National Park is one of Canada’s most popular wild swimming pools. Dolostone rock cliffs have eroded from below by centuries of waves, creating a sculptured overhang, beneath which the crystal clear waters of The Grotto glitter enticingly. It’s possible to camp at the park, but if you prefer four walls and modern facilities, check into the nearby Escarpment Heights Motel.

The To Sua Ocean Trench may not technically be underground, but it is in the ground enough to warrant being included in this list. Sunk 30-metres into the ground, this natural swimming pool is surrounded by lush gardens and accessed by a charming-yet-sturdy wooden step ladder. Spend a few hours floating in idyllic surroundings and finish your day by treating yourself to a massage at Saletoga Sands Resort & Spa.