Qinghai-Tibet Railway, China

Every other railway on this list seems like a cakewalk compared to the Qinghai-Tibet Railway, also known as the world’s highest railway. The first section of the railway was finished in 1984. Much of the railway, which connects China and Tibet, sits a staggering 13,000 feet above sea level, with some portions of the route even higher. Because of that, building the railway had more than its fair share of challenges, not the least of which was navigating the permafrost, lack of oxygen, and ecosystem. In fact, passenger cars are specially built to have enough oxygen for each passenger. Plus, each car has a doctor, and you need a health clearance to even take the train!

Above is a test train along the route.