The storm continued unabated during the first part of the night - at one point, enormous hailstones landing on the roof made it impossible to hear ourselves speak! And the last loud bang of thunder was just that: "Bang! Bang! Bang! Bang!" like that, before dying away. And so we slept, as the rain gradually petered out, too.
In the morning, it was still a bit cloudy, but we went out to explore the local Schloß on an island in what turned out to be the Traunsee.
After that, it was time to move on so we drove to Graz down a rather hairy motorway with lots of tunnels, which gave the sat nav indigestion! What slightly annoyed us was that yesterday we had bought our vignette to entitle us to drive on "All the motorways in Austria", as it says on the back, but twice there was a tollbooth where we had to pay again! Ah well, I suppose they have to pay for the tunnels somehow, but they might have warned us!
Anyway, eventually we got to the place in Graz where we are going to spend the night and found that, as we had been warned might happen, it was full. It is a Park'n'Ride, so we assumed it would get empty later (it hasn't much, so far), and decided that, because we were within reach of the Slovenian border, we would head down that way and visit the town of Maribor (Mauberg, in old money) before coming back.
We realised that we would have to buy a vignette for Slovenia, too, and we agreed we had rather "had" motorways for one day, so we came off at Leibnitz (which, alas, was not home to the eponymous biscuit, but was still rather pretty), and then continued on the slower roads to Maribor.
And a slow, and thundery, journey back - had to flash our passports at the frontier - but we found a parking space in the P&R and have parked up for the night.