Semmering railway

The Semmering railway in Austria, which starts at Gloggnitz and leads over the Semmering to Mürzzuschlag, was the first mountain railway in Europe built with a standard gauge track. It is commonly referred to as the world's first true mountain railway, given the very difficult terrain and the considerable altitude difference that was mastered during its construction. It is still fully functional as a part of the Southern Railway which is operated by the Austrian Federal Railways.

Source: Wikipedia