Some of the most amazing spectacles in this world are hidden deep underground, beneath rocks, sea and even ice. Many house cool attractions, some have a fascinating history, while others are simply mesmerising to look at.

Read on to see 29 of the world's most incredible caves and caverns you can actually visit...

Kentucky’s Mammoth Cave National Park is the world’s longest known cave system. It’s at least 400 miles (644km) long (an additional eight miles/13km was added in 2021), but there’s so much more that hasn’t even been explored. It’s easy to visit and free to enter the park, but you must pay for the cave tours (book in advance in summer).

Postojna Caves is Slovenia’s largest cave system, which spans over 12 miles (19km), with a quarter of that open to the public. You can walk the route, but there’s also a miniature train (opened in 1872) for a relaxing exploration of 2.2 miles (3.7km). Look out for the creepy, almost translucent olms, or “baby dragons", in the exhibition aquarium.

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Want to sleep on a Star Wars set? Then make like R2D2 and head to Hotel Marhala in Matmata, southern Tunisia. Some people in the Berber-speaking town still live in these traditional 'troglodyte' caves. Don’t expect luxury accommodation, this is the very definition of basic.

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While there are plenty of reasons to visit Luray – huge caverns, an incredible lake, ceilings that are 10 storeys high – the main reason is to hear the world’s largest musical instrument. The Stalacpipe Organ makes music by gently tapping stalactites. Buy your tickets in advance.

It’s not exactly a top tourist attraction, but Turkmenistan’s Door to Hell is pretty fascinating. Officially called the Darvaza crater, it was caused by a Soviet oil rig drilling into a natural gas cavern in 1971 and has been burning ever since. Take an off-the-beaten-track tour to visit while you still can, as it's been reported that the Turkmenistan president wants to extinguish the fire (natural gas is an important resource for the country).

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Waves crashing into solid calcium carbonate for 6,000 years is what created Chile’s incredible marble caves. Their swirling blue pattern changes colour and intensity throughout the year. You’ll need to join a boat tour to visit these caves as they’re in the middle of Lake General Carrera.

No one is really sure how Margate’s shell grotto came to be. It was discovered in 1835 by James Lovelock and his son, Joshua. They had been digging a duck pond at the time. It’s possible the grotto could have been the Victorian folly of a rich man, but some think it’s a smuggler’s cove.

Ice caves appear and disappear each year in Alaska's retreating Mendenhall Glacier and are notoriously difficult to reach. You can take a six- to eight-hour overland trek on a dangerous, unmarked trail or you can kayak across the ice lake (only for experienced cold water paddlers) and take a shorter hike. The glacier is around 13 miles (21km) from the town of Juneau.

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The view at Grotta Palazzese restaurant is nothing short of perfection. It’s built into a natural cave overlooking the Adriatic and the sunsets are as gorgeous as you’d imagine. Alas, there are reports of the restaurant experience not matching up to its surroundings. You can’t just grab a drink here and the cheapest meal (not including wine) will set you back around £168 ($212).

This huge and peaceful mountain cave temple filled with statues of Buddha is in the Phetchaburi province of central Thailand. It's only around 100 years old and was built in the reign of King Chulalongkorn. When the sun is shining, the light beams onto the stone and makes for a colourful sight. Just watch out for the pesky monkeys on the steep walk there.

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This beautiful cave off the northwest coast of Sardinia was discovered in the 18th century by a local fisherman. You'll find a white sandy beach inside that's almost a mile (1.6km) long. You can descend the 654 steps to the mouth of the cave but it’s far easier to get there by boat from the port of Alghero or the pier of Cala Dragunara in Porto Conte.

Washington’s Ape Cave is particularly interesting because it’s essentially a tube formed by lava. There are two options when you’re exploring. The upper cave is hard work, with some scrambling involved, and is 1.5 miles (2.4km) long. If you’re not a very experienced caver, try the lower one which is a one-way route that's less than a mile (1.6km) long. One more thing: don’t touch the walls, they’re covered in ecologically important slime.

Carlsbad Caverns in New Mexico is home to the Hall of Giants. It’s 4,000 feet (1,219m) long, 625 feet (190m) wide and 350 feet (106m) high, and it's the second-largest cavern in the world. You can explore the Natural Entrance Trail and the Big Room Trail on your own, but to venture further you need to join a ranger-led tour. 

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Capri, in Italy's Bay of Islands, is famous for its 'blue cave', where the sun illuminates the water from beneath the cave entrance and gives it that piercing bright blue colour. It’s a small cavern and dozens of wooden rowboats bring tourists here each day when the weather is good (early afternoon is the best time to see the blue at its most mesmerising).

Fingal's Cave is a sea cave just off the coast of the Scottish island of Staffa. There's nowhere else in the world like it – Mendelssohn was moved to compose an overture inspired by it and Sir Walter Scott called it "extraordinary". The hexagonal formations are so regular that some people assume it was made by hand, but it's actually all natural. In good weather, tours run regularly from Oban, Iona and the Isle of Mull.

You visit Waitomo Caves for one reason: the glowworms. You have to queue for a long time to get into the caves, but the boat trips are worth the wait, or if you're happy to get wet and climb through the caves you can explore on a rubber tube. Photos and taking videos is prohibited, so sit back and take in the luminescent light.

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Only a few miles outside of Kuala Lumpur, the Batu Caves are an important part of Malaysian history and culture. There are four caves to explore but the Temple Cave is the largest and most popular. They're also rumoured to have trapdoor spiders in them – a species that literally creates trap doors in the ground using soil – so watch your step. 

Cenotes (pronounced 'sey-no-tes') are natural sinkholes of various sizes – some are subterranean but others are flooded with sunlight because the roofs has long since caved in. Gran Cenote is on Mexico's Yucatan Peninsula, a limestone landscape famous for its cenotes. Here you pay an entry fee and you can swim, snorkel or go scuba diving. It gets crowded, so come early.

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Antelope Canyon in the Navajo Nation is the work of hundreds of years of sandstone erosion. There are two canyons to explore (Upper and Lower) and they're accessible by guided tour only. Go early to get the best photos and book your tour in advance.

Set in 65 acres of woodland, Carnglaze Caverns is a beautiful spot near the village of St Neot, Liskeard, that was originally a slate cavern. They really make the most of the natural acoustics with live music and comedy events, and best of all, you can get married here and say "I do" 200 feet (61m) underground.

Phraya Nakhon Cave in Khao Sam Roi Yot National Park is spectacular in its own right, but it's the little pavilion bathed in light inside which really makes it special. Want to visit? You've got quite the trek ahead of you: a boat ride, 1,450 feet (442m) of uneven and steep steps, then a slippery pathway into the cavern. Start early; the light in this beautiful cave looks best in the morning.

A result of the geothermal heat that Iceland is famous for, the Vatnajökull ice caves are a spectacle that wouldn't look out of place on a film set. Each summer, new crystal blue ice caves are formed in Europe's largest glacier and in the winter months they can be safely explored.

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Perhaps one of the most popular tourist spots in the Yucatán, Ik Kil is a cenote with an open top which lets in beautiful sunlight. There's a staircase down to the water so you can go for a dip – at one time it's thought this spot was used for human sacrifices.

Perhaps one of the lesser-known caves on the list, Saalfeld Fairy Grottoes in Germany is also one of the most spectacular. Water has been dripping through the soft rocks for years to create the colourful mineral formations. This one-time mine was re-discovered in 1913 and opened to the public a year later.

Remouchamps in the province of Liège in Belgium is hiding an incredible secret. This is where you'll find the world's longest subterranean river. After a half-a-mile (0.8km) walk exploring the passageways and cathedral cavern, you'll hop in a rowboat for a peaceful trip along the water. The caves were used in the Second World War as a shelter.

No stranger to visitors, Indian Echo Caverns in Pennsylvania has been a tourist attraction since the 1920s. The caves were probably used for storage and shelter and the limestone they're cut into is around 440 million years old. Bats, bears and raccoons have also made the cavern their home so keep a lookout.

In Spain's province of Málaga, these caves are home to famous rock paintings from the Paleolithic period (not open to the public), as well as the largest stalagmite in the world. You can visit on a self-guided tour – walk, drive or take the little 'train' from Nerja – or book an exclusive evening access tour.

The world’s largest cave, Son Doong, was only discovered and first explored in 2009. If you’re lucky enough to visit the cave in remote Phong Nha-Ke Bang National Park, you’ll find the longest stalactites in the world, limestone cave pearls and an underground rainforest. You can visit the cave on a four-day expedition from February to August, but tours must be booked well in advance. 

The aptly named Reed Flute Cave, near Guilin in southern China, is so-called because of the reeds that grow in the area that are used to make flutes. The caverns are lit with brightly coloured rainbow lights and collectively this place is known as the 'palace of natural art'. There are inscriptions here from as far back as the Tang Dynasty (AD 792).

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