Semmering (German pronunciation: [ˈzɛməʁɪŋ]) is a mountain pass in the Eastern Northern Limestone Alps connecting Lower Austria and Styria, between which it forms a natural border.

The project has now been revised according to the advanced state of technology and the layout of the line has been altered in order to minimize effects on ground water.

A ground-breaking ceremony was held at Gloggnitz on April 25, 2012 to officially launch preliminary construction works for the 27.3 km Semmering Base Tunnel.

It will eliminate the current bottleneck on the 41 km Semmering Railway route where steep gradients and numerous curves require freight trains to use two or three locomotives.

The Semmering ski resort, called Zauberberg, which also hosts World Cup events, is located at the pass and extends on to the Hirschenkogel mountain.