Before the Lærdal Tunnel was built, travel between Oslo, Norway's capital, and Bergen, its second-largest city, involved taking ferries or navigating treacherous, winding mountain roads ...

Maybe that's because it's also one of the world's steepest roads, chiseled into the mountain by local villagers. The Guoliang Tunnel is located in the Taihang Mountains in China's Henan Province ...

When it opened on July 4, 1930, it was the longest mountain tunnel in the U.S. Today, the sandstone tunnel is a major thoroughfare and top Zion National Park attraction. As you drive through it ...

One of the greatest concerns about such a long tunnel was driver fatigue and disorientation. Without proper design, a 24.5-kilometre drive underground could feel monotonous and even dangerous.