Tunnels have long been a source of intrigue for visitors, whether they are buried beneath oceans, hidden inside glaciers, or excavated well into the Earth. Beneath our feet lie hidden marvels of engineering: tunnels that snake their way deep below the Earth's surface, connecting cities, transporting goods, and facilitating essential infrastructure. These underground passageways, often overlooked but critical to modern life, have revolutionized transportation and urban planning. In this article, we will delve into the world of incredible tunnels, exploring their fascinating history, their modern applications, and the immense engineering challenges they present. 

These are the most incredible tunnels in the world, whether they're used to accelerate travel between big cities, bounce across islands, or even serve as a final resting place.

• Switzerland's Gotthard Base Tunnel

The Gotthard Base Tunnel is the world's longest and deepest railway tunnel, measuring 57 kilometers (35.5 miles).

This incredible engineering marvel should not be mistaken for the shorter Gotthard (road) Tunnel from the 19th century.  The Gotthard Base Tunnel was originally completed in 2016 to increase train freight traffic beneath the Alps.

Additionally, passenger services between significant continental and Swiss towns whiz by, passing depths of about 2,450 meters.

• Norway's Laerdal Tunnel

Norway relies heavily on tunnels to connect its numerous coastal cities and islands. It was completed in 2000. The Laerdal Tunnel, also known as Lrdalstunnelen, has provided the quickest route between Oslo and Bergen. At 24.5 kilometers (15.23 miles), it is the longest road tunnel in the world.

Engineers cut out rock chambers every six kilometers with special blue and yellow lights. Their designs resemble a sunrise, aware that the 20-minute trip would make drivers dizzy.

• France/UK Channel Tunnel

A subsea link between the UK and France has been planned for more than 200 years; daring 19th-century engineers even tried to drill beneath the English Channel to demonstrate its potential.

The 50-kilometer (31-mile) tunnel, which is 75 meters (246 feet) under the sea bed, was originally opened in 1994 after six years of development.

Today, the Channel Tunnel takes slightly over two hours to transport travelers between London and Paris. An automobile service allows drivers of cars and trucks to board trains close to the UK coastal town of Folkestone. Then, they get off at Calais on the French side.

• Japan's Tokyo Bay Aqua-Line

Japan has traditionally been a haven for tunnel builders thanks to its numerous islands and vast bays. Without having to navigate the coastline, the Tokyo Bay Aqua Line connects the prefectures of Kanagawa and Chiba. It is also known as the Trans-Tokyo Bay Expressway.

But what makes it unique is that it begins as a tunnel on the Kanagawa side before emerging from the ocean at Umihotaru, a man-made island with a rest area and platforms for admiring panoramic views of the Tokyo metropolis.

Arrivals at Haneda Airport will be able to see the bridge as their jet approaches to land over the ocean for the final stretch to Chiba.

• Japan's Seikan Tunnel

The Gotthard Base Tunnel may have surpassed the Seikan Tunnel in length, but the entire 53.85 kilometers (33.46 miles) of the Seikan Tunnel is still an impressive feat of engineering. It links Hokkaido in the north with Honshu, the biggest of Japan's islands.

Following a string of ferry catastrophes, it was first developed in the 1950s. It is now utilized for passenger trains, notably the Shinkansen bullet train that runs from Tokyo to Sapporo.

Domestic airlines have significantly reduced travel time, for hopeless romantics. It remains the best way to get to Japan's enchanted far north.

• Colorado's Eisenhonwer Tunel

The Eisenhower Tunnel is the tallest automobile tunnel in the country It carries vehicles from one side of the Great Divide to the other. The highest point of the tunnel is 3,401 meters (11,158 feet) above sea level. It makes it not only the tallest in the nation but also the tallest on the whole Interstate system.

In reality, it consists of two tunnels, one bearing the names of President Eisenhower and US Senator Edwin C. Johnson. The difficulty of building over the continental divide led to the discovery of fault lines during excavation.

• France/Switzerland Large Hadron Collider

The 27-kilometer (16.7 miles) long Large Hadron Collider was constructed specifically for particle acceleration. It lies on average 100 meters below the border between France and Switzerland. Two beams of particles are shot into the tube, where they impact at four different locations.

This state-of-the-art tunnel has helped physicists better understand the origin of mass. It has also helped to solve complex problems involving dark matter and dark energy.

You can visit CERN.  It is the European Organization for Nuclear Research which has an intriguing permanent exhibition about the collider's activity above ground. Note that you will need special permission to do so.

• Railway Jungfrau, Switzerland

The Jungfrau Railway weaves its way through a tunnel cut into some of the most recognizable mountains in the Swiss Alps, one of the great technical feats of the early 20th century.

Adolf Guyer-Zeller first had the idea in 1893, and it was finished in 1912. It begins at Kleine Scheidegg and ascends through a hand-cut tunnel into the heart of the Eiger, where two stations, Eigerwand and Eismeer, provide views of the mountain's north and east slopes.

Passengers can no longer exit at Eigerwand. Climbers have long been known to enter the tunnel through the iconic Stollenloch window, constructed to throw away garbage.

• Iceland's Langjokull Glacier Tunnel

The Langjokull Glacier Tunnel, billed as the greatest man-made ice structure in the world, is a two-hour drive from the capital, Reykjavik, into Iceland's second-largest glacier.

The ice turns more blue as visitors descend deeper into the slick depths, as the color of the ice changes with age.

There are guides available to answer questions on how the ice originated, what the future may hold for these phenomena, and to make sure that no one falls (crampons are available for securing hiking boots).

• China's Bund Sightseeing Tunnel

There are less expensive ways to travel between Shanghai's iconic Bund and the cutting-edge Pudong buildings. But this brief voyage on a Maglev train beneath the Huangpu River is a particularly surreal experience.

The purpose of strobe lights and sound effects is to simulate space travel. It depends on the traveler whether or not that's their reaction, but there's no denying it's an unusual way to navigate China's largest metropolis.

• Virginia's Natural Tunnel

The majority of railroad tunnels are the product of many years of laborious engineering and endure harsh operating conditions. However, Natural Tunnel is the result of a much slower process.

It is 61 meters wide at its widest point and 24 meters high at its highest point. It took over a million years for groundwater to dissolve the limestone and bedrock, causing it to form.

Because of this, the South Atlantic and Ohio Railroad decided to build a railroad through it in 1893. Today, the tunnel is the main draw of the State Park bearing its name. It also offers fantastic canoeing, hiking, and camping opportunities.

• Aussie Glow Worm Tunnel

The name of the gnat larvae that live on its ceiling and walls gave rise to the name of Glow Worm Tunnel, a lonely disused railroad tunnel in New South Wales' Wollemi National Park.

Since the 1940s, trains haven't run this way, giving the glowworms plenty of room to shine and entice prey.

Visitors are urged to bring a torch to illuminate the journey because the tunnel's almost 180-degree twist creates ideal, gloomy circumstances for these amazing creatures. Today, after traveling from Lithgow in the north, hikers can enter the tunnel.

• Vietnam's Cu Chi Tunnels

Tourists interested in learning more about the conflict that tore through Vietnam in the 1960s and 1970s have long been fascinated by this well-known network of tunnels on the outskirts of Ho Chi Minh City.

The tunnels were used as a base for Viet Cong assaults on US and South Vietnamese troops, as well as a place to live and store weapons.

The extensive network of 75 miles of tunnels survived despite numerous attempts by American soldiers to destroy them and is currently preserved as a memorial by the Vietnamese government.

Visitors can experience the cramped quarters firsthand and even visit the locations where the 1968 Tet Offensive was conceived.

• Kuala Lumpur, Malaysia's SMART

When considering how to drain stormwater away from Kuala Lumpur's downtown while also reducing traffic on the city's congested highways, Malaysian engineers came up with a brilliant solution: the stormwater management and road tunnel, or SMART.

SMART opened in 2007 and consists of a double-deck freeway and a rainwater bypass tunnel. It is the first dual-purpose tunnel in the world.

The road tunnel is also utilized to reduce the flow of floodwater into the Taman Desa reservoir. This is done if the rain is so intense that the water tunnel is at capacity. A series of downpours in the Malaysian capital in December 2021 led to an enormous five million cubic meters of floodwater being diverted by SMART.

• China's Guoliang Tunnel

To enable people to move from point A to point B, some tunnels delve deep inside mountains. However, the Guoliang Tunnel travels a much more picturesque route through China's Henan province.

It contains 30 windows that look down into the valley below, where building debris was dumped, and is carved out of the sheer cliff walls of the Taihang Mountains. This beautiful tunnel was constructed by just 13 Guoliang villagers to improve their village's connectivity with the outside world.

It's now one of the most popular tourist sites in China, but driving it requires a lot of guts. It has surprising curves, dips, and drops because it was hand-carved. And that's before you encounter vehicles traveling the other way.

• Iceland's Langjokull Glacier Tunnel

The Langjokull Glacier Tunnel, billed as the greatest man-made ice structure in the world, is a two-hour drive from the capital, Reykjavik, into Iceland's second-largest glacier.

The ice turns more blue as visitors descend deeper into the slick depths, as the color of the ice changes with age.

There are guides available to answer questions on how the ice originated, what the future may hold for these phenomena, and to make sure that no one falls (crampons are available for securing hiking boots).

• France's Paris Catacombs

Rocks were quarried for buildings throughout the French city in the 12th century. As a result, a large network of limestone mines was established beneath the Left Bank of Paris.

However, they didn't turn into an ossuary for the storage of human remains from Paris's overcrowded cemeteries until the late 18th century. Approximately six million bodies and their bones can be found in the catacombs today.

Tourists can still formally visit a tiny portion of the site, where a plaque cautions visitors about approaching "the Empire of Death." The site was initially accessible to the public in part in 1874 and was utilized by both the French Resistance and the Nazi occupiers in the 1940s.

The majority of the network is still restricted, though. Adventuresome travelers are nevertheless known to spend days underground, using the Metro tunnels and Left Bank basements to reach less-traveled areas.

• Norway's Drammen Spiral Tunnel

Drammen's Spiral Tunnel, which debuted in 1961 and underwent renovation in 2020, isn't your typical point-to-point underground route.

As its name implies, it ascends through six helix-shaped loops starting at its entrance, which is 50 meters above sea level, before emerging at 180 meters, where tourists may enjoy views of the nearby mountains and forest.

Pick up a Spiral Troll created especially for this occasion from coils of rope that resemble the tunnel itself.

The Historical Significance of Tunnels 

Tunnels have been around for centuries. Early examples date back to ancient civilizations such as the Egyptians and the Greeks. These early tunnels were typically dug for irrigation, mining, or defensive purposes. The Romans took tunnel construction to new heights, creating magnificent aqueducts and subterranean passageways.

Fast forward to the Industrial Revolution, and tunnels became instrumental in the development of transportation systems. The Thames Tunnel, completed in 1843, was the world's first tunnel. It was built for the sole purpose of accommodating pedestrians. The Thames Tunnel was a groundbreaking feat of engineering. It paved the way for the vast network of subways and underground railways we see today.

The Expanding Role of Underground Transportation

With the growth of urban areas and the increasing pressure on surface infrastructure, tunneling has become an integral part of transportation planning. Underground transportation systems, such as subways and metro networks, offer numerous advantages. These include reduced congestion, faster travel times, and improved connectivity.

Some of the most remarkable underground transportation systems include the London Underground, the Paris Métro, and the Tokyo Metro. These networks encompass extensive tunnel networks that span vast distances, often connecting the busiest parts of the city. 

Furthermore, tunnels play a crucial role in enabling high-speed rail systems. Examples are the Channel Tunnel linking the United Kingdom and mainland Europe, and the Seikan Tunnel in Japan, the longest undersea tunnel in the world.

Tunnels Enabling Infrastructure and Utilities

Tunnels are not limited to transportation; they also play a vital role in providing essential infrastructure and utilities. Underground tunnels are used to carry water, sewage, and gas,  minimizing disruption to urban landscapes and protecting vital resources from environmental factors. They also house electrical cables, fiber-optic networks, and other utilities necessary for modern life.

The Gotthard Base Tunnel in Switzerland, completed in 2016, showcases the monumental scale of modern tunneling projects. It is the world's longest railway tunnel, spanning 35 miles beneath the Alps. This engineering marvel greatly improves transportation efficiency. It reduces travel times and has a significant positive impact on the environment.

Challenges and Innovations in Tunnel Construction

Tunneling presents a unique set of challenges for engineers. Excavating through various geological formations, including solid rock, soil, and water, requires careful planning and innovative techniques. Safety considerations, such as preventing collapses and managing ventilation, are critical in tunnel design.

Recent advancements in tunnel construction have made significant strides in overcoming these challenges. Tunnel boring machines (TBMs) are now commonly used, capable of excavating tunnels efficiently and precisely. These machines can dig through various materials while simultaneously lining the tunnel walls, ensuring stability and minimizing disruption to the surface.

In addition, the development of advanced monitoring systems allows engineers to continuously assess the structural integrity of tunnels during and after construction. This real-time feedback ensures the safety and durability of these underground structures.

Conclusion

From ancient passageways to modern feats of engineering, tunnels have transformed the way we travel. They have also influenced the way we live, and interact with our environment. These underground networks play a crucial role in reducing congestion, connecting cities, and facilitating the flow of goods and utilities. Urbanization continues to grow, and our surface infrastructure reaches its limits. The development of underground tunnels becomes increasingly important.

The incredible tunnels pushing deep below the surface serve as a testament to human ingenuity, engineering prowess, and our ability to adapt to the challenges presented by our evolving world.

With ongoing innovations and the integration of new technologies, we can expect even more awe-inspiring tunneling projects in the future, further expanding our underground networks and shaping the cities of tomorrow.