I had a really bad running season and needed some some time on my own on the trails - FKT it is.
I researched the route for weeks to see if it is possible to do "unsupported" and was lucky to find public water sources at least every 10km, with only 1 exemption (I am happy to share the gpx track with the water sources with anyone wanting to try this route).
It starts in the middle of the historic city of Krems and leads to the rugged trails of Dürnstein via vineyard routes. The first half is mostly runnable, with very little technical terrain, but the technical parts are a welcomed alternation. After the "big" climb up to the Jauerling you can make up time around the city of Melk (which I can recommend to run at night). The most technical part is the Dunkelsteinerwald, with really beautiful single trails before you make your way back to Krems again via vineyards.
The last ~5km are pure torture, since you run on cobblestone and have to climb up and down to a historic church building with 100 stairs.