When the Bernina Express was planned, the engineers who built it were faced with a difficult challenge.
The train needed to bridge a considerable difference in altitude in a very short distance. The ride began in St. Moritz (1,775 m.a.s.l.), crossed the Bernina Pass (2,253 m.a.s.l.) and winds up in Tirano (429 m.a.s.l.). And since it was a train built specifically for tourists who wanted to see the lovely landscape, the train had to go through as few tunnels as possible. But the solution they came up with was quite ingenious: rather than use switchback tunnels, the train uses switchback viaducts that have have a diameter of 100 meters. Train passengers are usually in awe over this engineering feat.