Mysterious and often deadly, sinkholes are typically formed when the land above the surface collapses or sinks due to water erosion which causes the ground to crack and fall away. Global warming and volcanic activity can also cause them to emerge. From mystical blue holes and shimmering swimming spots to sprawling underground caverns and plunging pits, sinkholes can be as beautiful as they are terrifying. Here we take a look at some of the most incredible sinkholes around the world, in ascending order of depth – where measurements are known.

Tucked away from Spain's northern coastline in Asturias, Playa de Gulpiyuri is the smallest beach in the country and possibly the world. Stretching around 131 feet (40m) long (the depth is unknown), it was formed over centuries when the Cantabrian Sea chiselled away at the rocky coastline forming underground caves. One of the roofs of the caves collapsed creating a sinkhole that flooded. Separated from the sea by a 328 foot-thick (100m) cliff, at low tide the beach completely disappears, making it one of the region’s best-kept secrets.

Also known as Jackie’s Blue Hole, this water-filled opening in the South Pacific is one of Vanuatu’s most picturesque attractions. The Nanda Blue Hole was shaped by springs of fresh pure water rising to the surface which sliced a deep hole into the limestone rock. Shrouded by a lush jungle, the secluded lagoon is around 46 feet (14m) deep and is famed for its brilliantly blue water.

Montezuma Well is a detached area of the Montezuma Castle National Monument around 55 feet (17m) deep. Formed by a collapsed underground limestone cavern filled with water, the famous sinkhole has a rich history dating back to prehistoric times and was once the home of the Sinagua who left the area over 800 years ago. More than a million gallons of water are thought to flow through the well each day through a long narrow cave in its southeast rim, providing a lush green oasis in the middle of harsh desert grassland.

Set within northern Oman, the origin of this water-filled depression has been debated for years. Known as Hawiyat Najm which means Meteor Fall Park,  locals believe that a meteor fell in the spot where it lies. However, geologists have confirmed the sinkhole was caused by limestone erosion and rocks collapsing. With a pool measuring around 65 feet (20m) deep, the Bimmah Sinkhole is thought to be connected to the sea through an underground tunnel, which caused its striking crystal blue water.

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Also known as The Sunken Garden, this lush sinkhole on the southeast corner of South Australia was once a subterranean cave formed through the dissolution of limestone by seawater. The collapsed rock left a giant 66-foot-deep (20m) cavern filled with topsoil which in 1886, local farmer James Umpherston transformed into a gorgeous garden, hence the name. Today, Umpherston is home to a public barbecue and sculpture inspired by the geological processes of the region for visitors to enjoy in the day while the garden comes alive at night with possums feeding. 

Often considered to be one of the most unusual swimming holes on the planet, To-Sua is a sparkling jewel on the Samoan island of Upolu. Shaped during an ancient lava eruption after the land slipped away, it consists of two large holes linked by a lava tube cave. At 98 feet (30m) deep, the main hole, To-Sua, which translates to ‘giant swimming hole’ is filled with seawater, connected to the South Pacific by an underwater cave and fed by a series of tunnels and passages. Surrounded by lush native gardens, its enchanting crystal clear waters are one of the most photogenic spots in the region.

With its fiery red hot lava burning in the heart of a desert in northern Turkmenistan, the Darvaza Crater is often called “the Door to Hell”. The true origin of the surreal sinkhole is unknown although it’s thought that during the 1970s, Soviet Union scientists set the crater on fire to try and burn off toxic gases after the ground under a drilling rig gave way. At a whopping 223 feet (69m) wide and 99 feet (30m) deep, the mysterious molten pit has been spewing fire for decades and continues to baffle and intrigue people around the world.

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Unfortunately, not all sinkholes are naturally forming, as the Earth rapidly gets warmer, the growing threat of climate change is also a major cause for their appearance. For the past 15 years, more than 1,000 sinkholes have appeared around the Dead Sea on the coasts of Israel and Jordan as its water levels continue to drop. This has caused freshwater to diffuse into salt deposits beneath the surface of the shoreline, causing the earth above to collapse and form sinkholes. With some measuring hundreds of feet deep, the openings have swallowed up roads, palm fields and buildings and the amount seems to increase each year.

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Situated near the famous ruined Mayan city Chichen Itza, Ik-Kil is undoubtedly one of the most beautiful cenotes (geothermal sinkholes) in Mexico. Stretching around 131 feet (40m) deep and 197 feet (60m) wide, the opening was formed after a cave collapsed and filled with water thousands of years ago. Decorated with hanging ferns, green foliage and small waterfalls which trickle into the glittering blue pool below, Ik-Kil looks like something out of a fantasy novel. The cenote was considered sacred to the Mayans and is now used for swimming and diving.

In the southeast corner of South Australia, this pretty spot sits between two dormant volcanoes, Mount Schank and Mount Gambier. The sinkhole gets its name from its water which used to turn blue annually but, in recent years, has changed to a greenish colour. Bordered by rocky cliffs, the volcanic hole is about 131 feet (40m) in diameter, has a maximum depth of around 154 feet (47m), and is a much-loved swimming spot. 

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This deadly sinkhole in Alabama has earned a notorious reputation among climbers for its difficulty and being extremely dangerous. The Neversink Pit was formed when acid water eroded the rock beneath the ground, creating its dramatic 162 foot (49m) drop. With a 40-foot (12m) diameter, the only way to reach the bottom is straight down, and a permit is needed for climbing as well as proper equipment. Carpeted by a rare species of fern and pretty waterfalls which tumble down the rocks, the Neversink Pit is one of the most photographed natural wonders in Alabama.

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Hailed as one of the largest chasms in Europe, the Gouffre de Padirac (or the Padirac Cave) is a defining feature of France’s Dordogne Valley. Stretching 108 feet (33m) wide and dropping a staggering 246 feet (75m) below, we can see why it is called “the Devil’s hole” by locals. The spectacular sinkhole was crafted by a thousand years of underground water erosion which carved out its incredible limestone caverns filled with massive stalactites and stalagmites. A lift inspired by the Eiffel Tower takes visitors into its eerie depths and once underground, flat-bottom boats take passengers across a turquoise subterranean river. 

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Situated in the Brazilian city of Jardim, the Buraco das Araras is the most famous natural wonder in the state of Mato Grosso do Sul. Its name translates to Hole of Macaws, due to the flocks of colourful birds which nest and roost in the rock formation. The sandstone crater is thought to have been caused by a cave roof or boulders collapsing thousands of years ago. With a hefty estimated size of 328 feet (100m) deep and 1,640 feet (500m) in circumference, Buraco das Araras is South America’s biggest sinkhole. With the beautiful jewel-toned birds flying contrasting with the green vegetation which covers the upper part, it is a beautiful sight.

Plunging around 350 feet (106m) into the ground below, Devil’s Sinkhole in Texas is the largest single-chambered cavern in the state and has been a National Natural Landmark since 1968. Acidic water ate away at the limestone rock, causing the ceiling of the cavern to collapse and create a deep hole. Around three million Mexican free-tailed bats live in the sinkhole from May to October each year, and in the evening they form a tornado of bats as they leave the cave looking for food. The phenomenon is quite the spectacle, drawing tourists from across the country each year.

Considered one of the most stunning attractions of Australia’s Great Ocean Road, The Grotto beautifully frames the Victoria coastline. Hundreds of years of crashing waves and strong winds eroded the limestone cliffs, causing the rock to fall away towards the receding cliff line which created the caved sinkhole that can be seen today. The Grotto’s 394-foot (120m) cliff drops into the water below, creating a beautiful waterfall during the rainier seasons.

Egypt’s most infamous diving site, the Blue Hole can be found just off the country’s southeast coast, north of the town of Dahab. Plunging straight down into the watery depths of the Red Sea, the marine cavern is thought to be over 394 feet (120m) deep. Famed for being one of the most dangerous diving areas in the world, the Blue Hole has claimed the lives of numerous deep-sea divers who attempted to explore its depths. Plaques hang on the opposite cliffs commemorating those who have passed.

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Possibly the most famous underwater sinkhole in the world, the Great Blue Hole lies just off the coast of Belize in the heart of the Lighthouse Reef. Scientists believe that it may have formed during the last Ice Age, originally a limestone cave that flooded when sea levels rose. At over 984 feet (300m) wide and descending 410 feet (125m) into the Earth, it is the world’s largest sea hole and a popular scuba diving site. With its natural beauty and diverse marine life, the Great Blue Hole forms part of the UNESCO-listed Belize Barrier Reef Reserve System which is the largest barrier reef system in the Northern Hemisphere. 

Deep within Turkey’s Taurus mountains, with their sprawling size and mythical depths, these two sinkholes are known as Heaven and Hell. Cehennem (Hell) which is around 420 feet (128m) deep and Cennet (Heaven) which is 443 feet (135m) deep, were caused by underground waters melting the lime layer for years until it collapsed and emptied the water. According to Greek mythology, the king of the gods Zeus temporarily imprisoned Typhon, a 100-headed fire breathing dragon in Cehennem before taking him to Mount Etna. The main attraction is the ruined 5th-century monastery dedicated to the Virgin Mary that sits at the entrance of Cennet and is an eerie sight.

Stretching across a whopping 7,500 square miles (19,425sq km) near the Egyptian-Libyan border, the Qattara Depression is one of the biggest natural sinkholes on Earth. It formed over a thousand years, after salts in the soil eroded the rock into the sand which was blown away by Saharan winds, exposing the water table which is the boundary between water-saturated and unsaturated ground. At roughly 435 feet (133m) below sea level, the depression is as big as Lake Ontario and is the second-lowest point in Africa.

Puncturing the Moravian Karst cave system in the Czech Republic, the Macocha Gorge is the biggest of its kind in central Europe. Named the Macocha Abyss in the 17th century, the sinkhole is thought to have been created by the fallen ceiling of a huge cave, as rock debris has been found at the bottom. It is around 900 feet (275m) long and reaches a maximum depth of more than 453 feet (138m). A complex cave system can be found within the sinkhole while two platforms on the edges offer visitors epic views across the void.

Nestled on the coast of Long Island in The Bahamas, Dean’s Blue Hole is undoubtedly one of the most breathtaking underwater wonders on the planet. At a mighty 663 feet (202m) deep, the underwater sinkhole is the second deepest blue hole in the world. Enclosed by a natural rock amphitheatre on three sides, a sparkling white beach and lagoon beautifully frame the cavern. With its clear and calm waters, it is often hailed as one of the world’s best diving and snorkelling sites. 

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Located in Mexico’s Adama municipality, El Zacatón is a huge geothermal sinkhole (or cenote) intertwined in mystery and intrigue. The cenote was thought to be caused by a limestone rock collapse, and in 2007, a NASA-funded exhibition attempted to uncover the mysteries of its depths. An underwater robot was sent into the hole and even at around 984 feet (300m) deep, it was unable to reach its base. At an estimated 325 feet (99m) wide and 1,046 feet (319m) deep, El Zacatón is the biggest known water-filled cenote on Earth.

One of Mexico’s most incredible natural wonders, the Cave of Swallows can be found near the city of San Luis Potosi. The epic abyss gets its name from the swifts, parrots and swallows that live along its walls and was formed over millions of years by weather eroding the limestone rocks creating the cavern. Regarded as the largest cave shaft in the world, its depths reach around 1,680 feet (512m) while its mouth is around 197 feet (60m) in diameter. Its massive size has made it a popular destination for extreme sports enthusiasts including vertical cavers and base jumpers. 

This mystical karst lake within a sinkhole near the Croatian town of Imotski is intertwined in a terrifying myth. One of the deepest lakes in Europe, it is thought to be approximately 1,739 feet (530m) deep although its actual depth is unknown, the Red Lake is named after the red rocks that surround it. Legend has it that a local rich man called Gavan and his family were horrible and obsessed with wealth. An angel visited them disguised as a beggar asking for money and after his wife Gavanica refused, a violent tempest broke out, causing the ground to split open and form deep holes (the Red Lake and nearby Blue Lake) which swallowed up the family and their wealth. 

Xiaozhai Tiankeng lies in China’s Chongqing Municipality and holds the title of the biggest sinkhole in the world. Also known as the Heavenly Pit, the mammoth hole is a staggering 2,054 feet (626m) long and its depths are thought to reach up to 2,172 feet (662m), making it the deepest example on Earth. Formed over the limestone Difeng Cave which was carved out by an underground river possibly more than two million years ago, the sinkhole was discovered in 1994 by British explorers who accidentally stumbled upon it. Buried within its depths is a sprawling cave complex of corridors, stone pillars, cave pearls and halls, with a river trailing through it. 

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