Reported by Graham Rapier

For centuries, mountains and lakes posed massive problems for engineers.

In both cases, they make travel nearly impossible and can make trips longer by days or months to bypass obstacles.

However, with the invention of Marc Isambard Brunel and Thomas Cochrane's invention of the tunneling shield in the 19th century, that all began to change. Tunnels could go deeper - underwater through bedrock - allowing for quicker travel times.

From particle accelerators to portals through Switzerland's famous Alps, today's tunnels built with advanced Tunnel Boring Machines make Brunel's original London Thames tunnel seem tiny by comparison. For the purposes of our roundup, we excluded most metro tunnels, which are often built by cut-and-cover methods instead of boring, and water tunnels, which humans can't travel through (easily, at least.)

These are the world's 12 longest tunnels:

12. LEP Tunnel


Location: CERN, Switzerland/France, Europe

Length: 26.6km

Completed: 1988

Perhaps the most interesting tunnel on this list, the Large Electron-Positron collider tunnel is the only one on the list you'd have some trouble trying to travel through. Built in 1988, the tunnel at CERN's complex on the Franco-Swiss border has been the home to several particle accelerators used by nuclear researchers at the centre.

11. London Underground Northern Line

Oli Scarff/Getty Images

Location: London, England (from Morden to East Finchley)

Length: 27.7km

Completed: 1940

This portion of the Tube's Northern Line is still the United Kingdom's longest railway tunnel. Despite the exclusions of many other metro tunnels on this list, this portion makes the cut because the entire length was bored through solid rock beneath London's streets.

10. Taihang Tunnel

Location: Tailhang, China

Length: 27.7km 

Completed: 2007

9. West Qinling Tunnel


Location: Gansu, China

Length: 28km

Completed: 2016

8. Guadarrama Tunnel

Adrian Greeman/Construction Photography/Avalon/Getty Images

Location: Sierra de Guadarrama, Spain

Length: 28km

Completed: 2007

Spain's Guadarrama Tunnel carries high-speed trains on the Madrid to Barcelona train line.

7, New Guanjiao Tunnel

Wikimedia Commons

Location: Qinghai, China

Length: 32.5km

Completed: 2014

The New Guanjiao tunnel replaced an existing tunnel, built in the 1970's, through mountains in the rugged Tibetan plateau.

6. Lötschberg Base Tunnel

Wikimedia Commons

Location: Switzerland

Length: 34.4km

Completed: 2007

Lötschberg Base Tunnel was formerly the longest in the world until the Gotthard tunnel was completed nearly a decade later.

5. Songshan Lake Tunnel


Location: Dongguan, China

Length: 38.7km

Completed: 2016

4.Yulhyeon Tunnel

Media Handout

Location: Seoul, South Korea

Length: 50km

Completed: 2016

South Korea's Yulhyeon tunnel is virtually tied with the Channel Tunnel, and took more than three years to to carve the shortcut on the Korean peninsula.

3. Channel Tunnel

Location: English Channel, between England and France.

Length: 50km

Completed: 1994

While the Channel Tunnel has a longer underwater length than Seikan, its total length falls about two miles short of its Japanese counterpart.

2. Seikan Tunnel

Kyodo News via Getty Images

Location: Tsugaru Strait, Japan

Length: 53.6km

Completed: 1988

Seikan is the world's longest tunnel with an underwater segment, beating the Channel Tunnel in total length, but not in terms of how much is under water.

1. Gotthard Base Tunnel

Location: Swiss Alps, Switzerland

Length: 56.7km

Completed: 2016

The Gotthard base tunnel is the longest tunnel by distance and also the deepest. Read more about the tunnels history and construction here.

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