M56 Kolyma Federal Highway, Magadan to Yakutsk, Russian Federation
This 1,200-mile (1,931-kilometer) long route is known in Russia as the "Road of Bones." It was built between the 1930s and the early 1950s by thousands of prisoners from Soviet dictator Josef Stalin's Kolyma Gulag, who were deliberately overworked, starved to death and then buried beneath the route [sources: Travel + Leisure].
Never a dependable road surface, over the decades it has fallen into a worse state of disrepair, with vast unpaved, rut-laden stretches [source: BigEarthUK]. The Kolyma passes through some of the coldest inhabited places on Earth, with winter temperatures that drop to minus 70 degrees Fahrenheit (minus 56 degrees Celsius). At times, the road is frozen solid. But bizarrely, it's easier to travel the road when it's frozen in the winter than when it's a treacherous sea of mud in the summer [source: RoadTripsAcrossRussia.com]. To make matters worse, local officials warn that bandits have been known to attack unwary travelers [source: Gray].