The longest tunnel in the world extends 15.2 miles (24.5 km) between the cities of Laerdal and Aurland in western Norway. Known as the Lærdal Tunnel (or Lærdalstunnelen in Norwegian), the tunnel's construction lasted five years and was completed in 2000, surpassing the world's second longest tunnel, the St. Gottard Tunnel in Switzerland, by five miles.
Aside from its length, the Lærdal Tunnel is also the first to feature its own air treatment plant. Located in a 328-foot (100 m) cavern, the plant is comprised of two large fans and an electrostatic and carbon filter, which all work to remove dust and nitrogen dioxide from the large structure.
Since it takes the average driver 20 minutes to travel through the tunnel, special design features were added in order to prevent drivers from falling asleep. The tunnel is thus divided into four different sections that are broken up by "mountain caves." The mountain caves are 3.7 miles (6 km) apart and each one is equipped with special lighting that gives off the illusion of driving into daylight.
In the mountain caves visitors can stop to rest, make a U-turn, or even have a wedding ceremony, as one couple has done.