The first cave I ever explored was Postojna Cave in Slovenia, on a school trip when I was fourteen. I remember the train that takes visitors into the cave — a narrow-gauge electric railway that rattles through a tunnel in the limestone, emerging into a cavern so large that it had its own weather system. The stalactites hung from the ceiling like stone chandeliers, and the guide told us that some of them had taken hundreds of thousands of years to form, growing at a rate of about one centimeter per century. That fact lodged in my brain and has stayed there ever since: one centimeter per century. The patience of geology operates on a scale that makes human civilization look like a mayfly. Since that school trip, I've explored caves on every continent, and each one has reinforced the same sense of awe at the scale and slowness of the processes that created them.
Postojna Cave, Slovenia: The Classic
Postojna Cave, about fifty kilometers southwest of Ljubljana, is the most visited cave in Europe and one of the most impressive cave systems in the world. The cave extends for more than 24 kilometers, though only about 5 kilometers are open to the public. The visit begins with a 3.7-kilometer train ride into the cave, followed by a 1.5-kilometer guided walk through the most decorated sections. The train ride alone is worth the visit — the cave passages are large enough to accommodate the train comfortably, and the limestone formations are visible from every window. The train passes through the Massive Hall, a cavern 130 meters long, 40 meters wide, and 45 meters high, before arriving at the Great Mountain, where the walking tour begins.
A walking tour passes through a series of chambers, each with its own distinctive formations. The Brilliant Hall contains stalactites and stalagmites that are pure white, formed by calcite-rich water dripping from the ceiling over millennia. The Spaghetti Hall is filled with thin, straw-like stalactites called helictites, which grow in curving, twisting patterns that defy gravity — they are formed by capillary action drawing water through tiny pores in the rock, rather than by dripping. The Concert Hall, a large chamber with excellent acoustics, has been used for underground concerts for more than a century. The tour is led by knowledgeable guides who explain the geology and history of the cave in multiple languages. The entrance fee is 30.80 euros for adults, and the tour takes about ninety minutes.
Postojna Cave is also home to the olm (Proteus anguinus), a blind, cave-dwelling amphibian that lives only in the underground rivers of the Dinaric Alps. The olm is sometimes called the 'human fish' because of its pale, pinkish skin, and it can live for up to 100 years and survive for up to 10 years without food. The olm is not visible on the standard cave tour, but the cave's Vivarium, located at the entrance, has a display of live olms in aquariums. The Vivarium is included in the entrance fee and is worth spending fifteen minutes in before or after the cave tour. Postojna is easily reached by train from Ljubljana (about one hour) or by car (about forty-five minutes). The cave is open daily year-round, and the temperature inside is a constant 8 to 10 degrees Celsius — bring a jacket regardless of the season.
Waitomo Glowworm Caves, New Zealand
The Waitomo Glowworm Caves, on New Zealand's North Island about two hours south of Auckland, are famous for the thousands of glowworms (Arachnocampa luminosa) that illuminate the cave ceilings like a starry sky. The glowworms are the larvae of a species of fungus gnat that is found only in New Zealand, and they produce a blue-green bioluminescence to attract prey — small insects that become trapped in the sticky silk threads the larvae hang from the cave ceiling. The effect, when viewed from a boat on the underground river that runs through the cave, is magical: the ceiling above you is covered with thousands of tiny blue lights, reflected in the dark water below, creating the impression of floating in space.
The standard cave tour costs 62 New Zealand dollars ($37) and lasts about forty-five minutes. The tour begins with a walk through the upper levels of the cave, where the guide explains the geology and the glowworm life cycle, and ends with a boat ride through the Glowworm Grotto, the section of the cave with the highest concentration of glowworms. Photography is not permitted in the Glowworm Grotto — the light from cameras and phones can disrupt the glowworms' feeding behavior — which is frustrating but understandable. The boat ride is silent (the boat is pulled by a guide using an overhead wire, not motorized), and the darkness and silence make the glowworm display even more immersive.
For a more adventurous experience, the Waitomo company offers several options that go beyond the standard tour. The Black Abyss tour ($265) includes abseiling (rappelling) into the cave, climbing, and tubing through the underground river. The Lost World tour ($325) involves a 100-meter abseil into a massive shaft and several hours of cave exploration. I did the Black Labyrinth tour ($195), which includes tubing through the cave river in the dark (you wear a helmet with a headlamp, but much of the route is in complete darkness), climbing through narrow passages, and jumping off small waterfalls. The tour lasts about three hours and requires a reasonable level of physical fitness — you'll get wet, cold, and muddy, and you'll love every minute of it.
Mammoth Cave, Kentucky: The World's Longest
Mammoth Cave National Park, in central Kentucky, contains the longest known cave system in the world, with more than 680 kilometers of surveyed passages. The cave has been known to humans for at least 4,000 years — Native American artifacts found in the cave date back to the Archaic period — and it has been a tourist attraction since 1816, making it one of the oldest tourist attractions in the United States. The scale of the cave is difficult to comprehend: the surveyed passages, if laid end to end, would stretch from Louisville to Nashville and back.
The National Park Service offers a range of guided tours, from easy walking tours to strenuous crawling tours. The Historic Tour ($18 for adults) is the most popular option, covering about 3 kilometers of passages over two hours. The tour passes through the Rotunda (a large entrance chamber that has been used for events since the 19th century), the Bottomless Pit (a 35-meter-deep shaft), and Mammoth Dome (a massive column of flowstone 20 meters high). The Frozen Niagara Tour ($17) focuses on the cave's most decorated section, where stalactites, stalagmites, and flowstone formations cover the walls and ceiling in Complex patterns. For more adventurous visitors, the Wild Cave Tour ($65) is a six-hour, physically demanding tour that involves crawling through tight passages, climbing over breakdown blocks, and getting thoroughly muddy.
I took the Historic Tour and the Frozen Niagara Tour on the same day, which gave me a good overview of the cave's variety. The Historic Tour is impressive for its scale — the passages are enormous, and the sense of being inside a mountain is visceral. The Frozen Niagara Tour is impressive for its beauty — the formations are delicate and colorful, with shades of white, orange, brown, and red created by different mineral deposits. The cave temperature is a constant 13 degrees Celsius (54 degrees Fahrenheit) year-round, and the humidity is near 100 percent. Wear sturdy walking shoes with good traction — the cave floors are wet and slippery in places — and bring a light jacket. The park has a campground ($20 per night) and a lodge (rooms from $95 per night) for visitors who want to spend more than one day.
Carlsbad Caverns, New Mexico: The Underground Big Room
Carlsbad Caverns National Park, in southeastern New Mexico, contains one of the largest and most decorated cave chambers in the world: the Big Room, a limestone chamber 1,800 feet long, 1,100 feet wide, and 255 feet high at its highest point. The Big Room is so large that it could contain six football fields, and its ceiling is covered with stalactites, stalagmites, columns, soda straws, and other formations that range in size from delicate, thread-like tubes to massive columns that weigh hundreds of tons. The Natural Entrance trail, which descends 230 meters from the cave entrance to the Big Room via a series of switchbacks, is one of the most dramatic approaches to any cave in the world.
This park offers two self-guided tours: the Big Room Trail ($15 for adults) and the Natural Entrance Trail ($15). I did both, starting with the Natural Entrance Trail in the morning and the Big Room Trail in the afternoon. The Natural Entrance Trail descends through a series of switchbacks carved into the cave entrance, passing the Bat Cave (a section where hundreds of thousands of Brazilian free-tailed bats roost during the summer months) and the Devil's Spring (a pool of water that reflects the cave formations above it). The descent takes about forty-five minutes and is moderately strenuous — the trail is steep and the humidity is high. An elevator provides an alternative route to the Big Room for visitors who don't want to make the descent.
The Big Room Trail is a 1.6-kilometer loop on a paved trail that circles the perimeter of the Big Room. The trail is mostly level and accessible to visitors with mobility limitations. The formations along the trail include the Giant Dome (a massive column 19 meters tall), the Bottomless Pit (a 110-meter-deep shaft), the Rock of Ages (a flowstone formation that has been dated to 260 million years), and the Chinese Theater (a section of the cave where the formations resemble theatrical scenery). I spent about ninety minutes on the Big Room Trail and could easily have spent longer. The cave is open daily year-round except December 25, and the temperature inside is a constant 13 degrees Celsius. The park's evening Bat Flight Program, held from May through October, allows visitors to watch the bats emerge from the cave entrance at sunset — a spectacular natural event that is free to attend.
Jeita Grotto, Lebanon: An Underground Cathedral
The Jeita Grotto, about twenty kilometers north of Beirut, consists of two separate but connected limestone caves: the Upper Grotto and the Lower Grotto. The Upper Grotto is accessed by a walkway and contains some of the most spectacular stalactites and stalagmites I've seen in any cave — the formations are massive, colorful, and so numerous that the cave feels like an underground cathedral. The Lower Grotto is accessed by a boat ride on an underground river that runs through the cave, and the experience of floating through the darkness with the cave walls reflected in the still water is hauntingly beautiful.
When combined ticket for both grottos costs 33,000 Lebanese pounds ($22). The Upper Grotto tour takes about one hour and follows a concrete walkway through a series of chambers. The formations include the 'Pantheon' (a chamber with columns that resemble a classical temple), the 'Minaret' (a thin, towering stalagmite 8 meters tall), and the 'Curtain' (a massive flowstone formation that hangs from the ceiling like a stone drapery). The Lower Grotto tour takes about thirty minutes and is conducted in small boats that seat eight passengers. The boat ride follows the underground river for about 600 meters, passing through chambers with names like the 'Lake of Legends' and the 'Echo Chamber.' The boat ride is silent and atmospheric, and the reflections of the cave formations in the water double the visual impact.
Jeita Grotto was a finalist in the New7Wonders of Nature competition and is one of Lebanon's most important tourist attractions. The cave is well-managed and well-maintained, with good lighting, safe walkways, and informative signage in multiple languages. Photography is permitted in the Upper Grotto but not in the Lower Grotto (to prevent camera flashes from disturbing the boat ride experience). The cave is open Tuesday through Sunday (closed Mondays) from 9 AM to 6 PM. The temperature inside is about 16 degrees Celsius in the Upper Grotto and 22 degrees Celsius in the Lower Grotto. A jacket is recommended for the Upper Grotto. The Shape from Beirut takes about forty-five minutes by car or taxi.
Safety and Preparation for Cave Exploration
Cave exploration is generally safe when done through organized tours at developed show caves, but there are some basic precautions that every visitor should take. The temperature inside caves is consistently cool (8 to 15 degrees Celsius in most cases) and the humidity is near 100 percent, which means you'll feel colder underground than the temperature alone would suggest. Bring a jacket or sweater, even in summer. Wear sturdy walking shoes with good traction — cave floors are wet, uneven, and can be slippery. Many caves have standing water or shallow streams that you'll need to walk through, so waterproof shoes or shoes that you don't mind getting wet are ideal.
For more adventurous cave tours that involve crawling, climbing, or swimming, a reasonable level of physical fitness is required, and you should follow the guide's instructions carefully. Never enter a wild cave (one without developed paths and lighting) without proper training, equipment, and companions. Wild caving is a technical activity that requires helmets, headlamps, backup light sources, and knowledge of the cave system. The National Speleological Society (caves.org) provides information about caving clubs and training courses in the United States, and similar organizations exist in most countries. If you're interested in wild caving, start with a guided trip through a reputable outfitter before attempting to explore caves independently.
Some medical conditions require special consideration for cave visits. People with claustrophobia should be aware that many cave passages are narrow and enclosed, and some tours require crawling through tight spaces. People with heart conditions or respiratory problems should check with their doctor before visiting caves, as the physical exertion and the high humidity can be demanding. If you have any concerns, contact the cave's visitor center in advance to discuss the physical requirements of the tour you're planning. Most show caves have options for visitors with mobility limitations, including paved walkways and elevator access.
