Krimmler Wasserfaelle are not far from Zell am See
Krimmler Wasserfaelle are a great halfday-excursion from Zell am See. They are the highest waterfalls in Austria.It needs a lot of walking uphill and downhill for quite some time in order to see at least a small part of these gigantic waterfalls. You will mostly see just a small part of it and in order to see all of the many cascades at the same time in your photos you have to step up one of the mountains opposite of the falls or even better : take an airplane (e.g. from Zell am See).
Nevertheless it is worth to step up at least to the 2nd viewpoint, the view from there is excellent, but the haze of the water is sometimes taken to the viewpoint by the wind, so take care of your camera and a rain-gear is never really wrong at these waterfalls, even in bright sunshine !
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Krimml is quite easy to drive to, when you are coming from Zell am See and Mittersill, the road is also quite scenic.
By public transportation you can take the Bus #670 from Zell am See, it starts in front of the train-station and it also is a ÖBB-bus, so it will be included in your train-passes.
The ride from Zell am See to the village of Krimml takes 75 minutes and the station of the bus is rather close to the entrance of the Krimmler Wasserfaelle.

Zell am See: Hundertwasser's Austria-fountain
Elisabethkapelle auf der Schmittenhöhe
The gush that sources the river Danube.
Pasterzenglacier