Here's a map with the route I used to get to and from Mariazell.
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Apple Maps
The bold blue line shows my route, except for the last part, where I was driving the roads marked by the red line.
Here's where I stopped to take pictures:
1 - Schottwien Bridge
2 - Mürz, Totes Weib
Well, actually I didn't stop at the bridge, but in a village from where you can see it well enough to take photos, which was Maria Schutz.
The bridge itself is made of concrete, 250 metres long, connects two tunnels, and the road is 130 metres above the ground, above a municipality called Schottwien. That's also the reason why it's called the "Schottwien Bridge", or "Talbrücke Schottwien" in German - it crosses a valley near Semmering. It was built from 1986 to 1989.
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I tried to get a view of the bridge without too many trees and bushes, but that wasn't really possible.
This image from Herbert Ortner (Wikimedia) shows better what it looks like:
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You don't really realize that you're on the bridge, actually. The motorway is broad, so you can't take a look at the valley below. Which is good, imo, or some drivers would refuse to use the bridge, and I would be one of them.