Buzz
Earth's mountain ranges and skies have long been home to awe-inspiring vistas, iconic landmarks, and unforgettable feats. Yet, what lies beneath the surface is just as extraordinary. Across the globe, natural caves and human-made shafts hold their own remarkable stories.
10. Y-40 Deep Joy
Do you recall the childhood challenge of trying to touch the bottom of the deep end of a public swimming pool? Now, imagine reaching the bottom of a pool that is about 10 times deeper, and you have the Y-40 Deep Joy Pool in Montegrotto Terme, Italy. As part of the Terme Millepini Hotel, the Y-40 holds the title of the deepest swimming pool on Earth, with a vertical shaft plunging 42 meters (138 feet) deep and holding 4.3 million liters (1.1 million gallons) of water.
The Y-40 is much more than just a deep diving hole. The shaft is only a portion of this extensive pool, which also includes flat areas at varying depths, such as a more conventional 1.3-meter (4-foot) shallow end, along with several artificial underwater caves. The water itself comes from local hot springs and is kept at a comfortable 33 degrees Celsius (91 °F), allowing divers to enjoy the pool without needing a wetsuit. Furthermore, there is a transparent viewing tunnel at a depth of 5 meters (16 feet), offering an opportunity to view the deeper sections without getting wet, much like the viewing tunnels found in aquariums.
9. Eiksund Tunnel
The Eiksund Tunnel in Norway passes beneath Vartdals Fjord, connecting Hareidlandet Island with the mainland. Opened in 2008 as part of the Eiksundsambandet Project, which also included several other tunnels and a bridge, the tunnel provides a permanent link between Hareidlandet and the rest of the country. Like many tunnels worldwide, Eiksund significantly reduces drivers’ reliance on ferries and overall travel time. The tunnel reaches a maximum depth of 287 meters (942 feet) below the surface, making it the deepest underwater tunnel for driving in the world.
Building the 7.8-kilometer (4.8 mi) tunnel required digging through 660,000 cubic meters (23 million ft) of rock, enough to fill a football field to a height of 175 meters (574 feet). Located under a fjord, the Eiksund Tunnel also has steeper gradients than most tunnels. This has been known to discourage some drivers, possibly due to a proven link between steeper tunnel gradients and a higher rate of accidents.
8. Dragon’s Breath Cave
Situated in Namibia’s Kalahari Desert, Dragon’s Breath Cave earns its name from the warm, humid air that flows from its entrance. In 1986, it was discovered that this humidity was caused by a vast underwater lake located approximately 60 meters (197 feet) below the surface. The lake spans around 2 hectares (5 acres), making it the largest known underground lake in the world that isn't trapped beneath a glacier. Though difficult to access, the lake's maximum depth remains unknown, with the deepest recorded point being 91 meters (300 feet).
The incredibly clear and calm waters of the lake are home to one of the rarest fish species in the world, the golden cave catfish. This air-breathing species is found exclusively in Dragon’s Breath Cave, where it feeds on any organic matter that falls into the water. Only about 150 of these catfish are thought to remain in the lake, making them critically endangered. These fish are devoid of pigment and have small, nonfunctional eyes that are covered in skin due to the complete absence of natural light.
7. Great Pagosa Aquifer
The Springs Resort and Spa in Pagosa Springs, Colorado, boasts several geothermal soaking pools. For many years, visitors have flocked to these pools, attracted by the reputed healing effects of the water's high mineral content. The mineral concentration is so significant that visitors are cautioned that drinking directly from the pools may have a laxative effect. It is advised to allow the water to settle before decanting it.
The Springs Resort and Spa in Pagosa Springs, Colorado, is supplied by the Great Pagosa Aquifer, locally known as the 'mother spring.' This natural hot spring is far too hot for direct bathing, with temperatures averaging 55 degrees Celsius (131 °F) at the surface. Underground pipes channel the mother spring's water to various soaking pools at the resort, which are kept within a more manageable temperature range of 28 degrees Celsius (83 °F) to 46 degrees Celsius (114 °F). Visitors are advised not to soak for more than 10 minutes at a time.
The mother spring has an average depth of 8 meters (25 feet), but in the center, the geothermal waters rise from a much deeper opening. The hole at the bottom of the spring has been officially measured at 305 meters (1,002 feet), making the Great Pagosa Aquifer the deepest geothermal hot spring in the world. While this is the officially recorded depth, the true depth is still unknown, as the measuring line ran out at 305 meters (1,002 feet) without reaching the bottom.
6. El Zacaton
Located in Tamaulipas, Mexico, El Zacaton is the world's deepest water-filled sinkhole. The hole spans 116 meters (381 feet) in width and is surrounded by steep 20-meter (66-foot) cliffs leading down to the water's surface, which has been measured at a depth of 319 meters (1,047 feet). A true sinkhole, El Zacaton was formed through volcanism, which heated and acidified the groundwater beneath the site, causing it to rise and dissolve the limestone above. This geothermal activity keeps El Zacaton's water at a steady 30 degrees Celsius (86 °F).
El Zacaton is named after the zacate grass that grows around one of its most distinctive features: floating islands. These islands, possibly created by the sinkhole's volcanic activity, float on the surface as carbon dioxide brings minerals to the top. Their lightweight nature allows the wind to move them across the water.
The sinkhole is also a prominent site for both diving enthusiasts and scientific research. Most divers enter Zacaton through a 17-meter (56-foot) underground tunnel leading from a nearby spring, instead of descending the steep cliffs surrounding the surface. Zacaton has been the location of several scuba diving records, though tragically, a diver lost their life when their partner couldn't see that something was wrong due to the darkness, with only the diver's light visible. Additionally, extremophile bacteria have been discovered at the bottom of Zacaton, thriving on sulfur.
5. Superconducting Super Collider
The Superconducting Super Collider (SSC), once an ambitious project, would have been an enormous particle accelerator with a circumference of 87 kilometers (54 miles), circling the town of Waxahachie, Texas, just south of Dallas. Unfortunately, the project faced significant cost overruns, leading to its eventual abandonment before completion.
The Superconducting Super Collider project was authorized in 1987, initially projected to cost $4.4 billion, funded primarily by the US Department of Energy and the state of Texas. By 1993, the overall cost estimate had escalated to $11 billion, prompting the US Congress to officially cancel the project. At that point, $2 billion had already been invested, and 24 kilometers (15 miles) of tunnel had been dug. Today, the tunnels serve as a reservoir for rainwater.
The abandoned Superconducting Super Collider is often referred to as 'the most expensive hole ever dug in human history.' Some argue that, had the SSC been completed, the discovery of the Higgs particle could have occurred sooner, potentially allowing the US to retain its lead in particle physics research.
4. Vrtoglavica Cave
Vrtoglavica Cave, also spelled 'Vrtiglavica,' is nestled near the Italian border in Slovenia’s Julian Alps. The entrance, covered in ice, sits 1,900 meters (6,234 feet) above sea level on Mount Kanin.
The name 'Vrtoglavica' translates to 'cave of vertigo' in Slovenian, a fitting description. The narrow, almost vertical passage that leads into the cave is treacherous, with smooth, ice-coated walls. Eventually, the passage opens into a vast, deep pit.
While not the largest, longest, or deepest cave, Vrtoglavica Cave is remarkable for containing the world’s longest uninterrupted vertical drop. An object (or caver) can fall freely for 603 meters (1,978 feet) before reaching the bottom. The cave also houses one of the longest underground waterfalls, stretching approximately 420 meters (1,378 feet). This waterfall originates from several horizontal passages that emerge from the cave’s walls, and the water continues its journey deeper underground.
3. TauTona Mine
TauTona, meaning 'great lion' in Setswana, is a South African gold mine that has been active since 1962. In 2006, the mine underwent an expansion, adding more shafts to its original 2-kilometer (1.2 mi) main shaft. By 2008, the project was completed, with TauTona’s lowest point reaching 3.9 kilometers (2.4 mi) beneath the surface, making it the deepest mine in the world. It takes about one hour to travel from the surface to the bottom by elevator.
This vast structure includes approximately 800 kilometers (500 mi) of tunnels, where 5,600 miners work under hazardous conditions. One major risk is the extreme temperatures at the deepest levels of the mine. The air temperature can reach 55 degrees Celsius (131 °F), while the rock face can reach 60 degrees Celsius (140 °F). Air conditioners help maintain a more comfortable working temperature of 28 degrees Celsius (82 °F).
In recent years, TauTona’s gold production has decreased significantly, dropping from 13,437 grams (474 oz) in 2006 to 5,358 grams (189 oz) in 2012. This decline is partly due to increased seismic activity, which disrupted mining operations and required changes to mining strategies. Fortunately, the price of gold has generally risen since 2006.
2. Gastein Healing Cave
Located in Austria's Gastein Valley, the Grand Park Hotel and Spa is home to the world’s largest pain management center. It draws patients suffering from chronic conditions such as arthritis, fibromyalgia, gout, and other persistent illnesses to its Heilstollen, or 'healing cave gallery,' inside Radhaus Mountain. Many visitors claim that their time in the cave brings lasting relief from their discomfort, with the Gastein Healing Cave boasting a remarkable success rate of 90 percent.
What makes the Heilstollen so effective? The key lies in the natural heat, humidity, and radon gas found within the cave. Radon exposure is recognized as the second leading cause of lung cancer.
Patients journey about 2 kilometers (1.2 mi) into the mountain for 60-minute sessions within one of five chambers. The conditions inside range from 37°C (98.6°F) with 75% humidity to 41.5°C (106.7°F) with 100% humidity. The radon is absorbed through the lungs and skin, where it emits alpha radiation that is believed to promote cellular repair, reduce inflammation, and trigger the release of endorphins. The heat of the cave’s chambers is thought to enhance the radon’s therapeutic effects. Patients are advised to drink plenty of water beforehand, and pregnant women are prohibited from entering the cave.
No level of radon gas is considered safe. Despite this, the Gastein Healing Cave is widely accepted as a form of therapy and has been in operation since 1952. In fact, health insurance plans in both Germany and Austria even cover sessions at the cave.
1. Woodingdean Well
In 1858, the town of Woodingdean, England, embarked on plans to build a new structure at a nearby industrial school for troubled youth. A reliable water source was necessary, but pumping water from distant locations was deemed too costly. Thus, the construction of Woodingdean Well was initiated, with adult laborers from a local workhouse recruited to help reduce costs. The digging was done entirely by hand, with earth hoisted to the surface using hand-winched buckets.
The original plan called for a 122-meter (400 ft) brick-lined well. After two years of digging, the well had reached 134 meters (438 ft) below the surface, slightly beneath sea level, yet still no water had been found. To address the issue, horizontal shafts were excavated in four directions, but this approach also yielded no results. The project leaders refused to concede defeat, instructing the team to start a new vertical shaft at the end of one of the horizontal ones.
For another two years, a vertical shaft was dug, with workers toiling around the clock to dig and lay bricks. The only illumination came from candles, and the cramped conditions led many workers to labor without clothes. At long last, on March 16, 1862, a bricklayer noticed the ground at the bottom slowly rising. After a tense 45 minutes, the workers scrambled out of the well just as water surged upwards, marking the long-awaited success. After four years of relentless effort, the Woodingdean Well had reached an astonishing 392 meters (1,285 ft) deep, making it the deepest hand-dug well in the world.
