Just a few kilometers from the flat you will find the Krimmler Falls; one of the largest tourist attractions in Austria. And - quite rightly so; the waterfall is breathtakingly beautiful. You can take a beautiful walk from Krimml along the waterfall. You can see the waterfall up close from various viewpoints. Be prepared though - you have to climb 700 meters.
If you really want a superb trip: take two days to walk through the valley (by the way, with 20 km lenght, the longest trafiic-free valley in Austria) to the Tauernhaus; where you can spend the night. Return the next day.