I visited this WHS in July 2017. I completed all Austrian WHS with this trainspotting visit so as such it will always have a special place in my memory.

The Semmering Railway was built between 1848 and 1854 under the supervision of Carl Ritter von Ghega. It is the world's first high mountain railway and is part of the Sudbahn which stretches from Vienna to Trieste. It reaches from Gloggnitz to Murzzuschlag over a distance of 41.8km, crossing the Semmering (984m).

The numerous gorges, rift valleys, rock faces and mountain ridges had to be made accessible for rail traffic by 15 tunnels, 16 viaducts and 100 bridges. By car (and some pleasant hiking trails), I saw the Haupt tunnel, the Kartner Kagel tunnel, the Weberkagel tunnel, the Polleres tunnel and viaduct, the Krausel tunnel and viaduct, the Semmering railway station, the Breitenstein viaducts and the Kalte rinne (790m) along the Semmering Hochstrasse and Bahnwanderweg.

The highlight of my visit was hiking along the Bahnwanderweg (around 1 hour hike on the Spiestal-Breitenstein trail) and trainspotting at the scenic 20 Schilling panoramic viewpoint of Breitenstein. I parked my car next to the Kunst + Technik Skulpturen Park and there is a small trail which starts right behind the small football pitch there. I was surprised to find out that trains (both passenger and cargo trains) pass through the single rail Breitenstein viaduct from both directions so they are timed to pass at different intervals to allow safe passage through the rather busy railway.

There are information boards in English and German at most viewpoints and at every significant railway infrastructure. I also visited the Semmering Railway Information Point and Museum which is open daily from 9am till 3pm. There is a UNESCO WHS inscription plaque at the railway station just in front of the only fountain.

All in all, this WHS is rather similar to the Rhaetian Railways WHS and quite an interesting WHS. To really appreciate the railway infrastructure though, I would recommend going on some pleasant hiking trails instead of spending a lot of money on a train ticket. You won't be able to see much of the railway infrastructure if you're on the train but rather passing on it or through it perhaps without even knowing!