The hiking trail through the Proßeggklamm was closed for a long time and has been rebuilt. The winding path leads through short tunnels and through the gorge with impressive views. Many parts of the narrow path are secured with ropes as it drops almost vertically into the depths. A sign at both entrances warns of the dangers, including the danger of falling rocks in some sections (if you like, you can borrow a helmet from the Matrei tourist office for a 5 euro deposit). In theory, a via ferrata set can also be used at the rope-secured sections. However, if you are sure-footed and have a head for heights, you won't need this in normal weather. According to the internet, the passage is "forbidden" for children under 10 years of age, but the signs on site recommend that children be roped up. As a fall from the path can be fatal, this seems sensible depending on the age and level of understanding and sure-footedness. Small children will not always be able to reach the ropes; the path is too narrow for them to walk next to each other. It is not without reason that it is pointed out that this is a path and not a walking path. So decent shoes are also recommended. We (mountain-experienced but small "climbers" or alpinists) relaxedly hiked through the gorge with our dog in dry conditions and were able to fully enjoy the path and the view.
The passage is free. You can reach the gorge from Matrei along the Tauernbach (worth it!) or park near the gorge entrance on the edge of Proßegg.
Conclusion: It's worth it!