I did this ride a few weeks ago with a Swiss friend of mine.  Easy train ride from Vienna and then a great ride along the Danube - the most popular cycling route in Europe.  I am close to having ridden the whole river in Austria - just lacking about 25 miles from Linz to Ybbs!  This ride was through the Wachau valley which is spectacular, replete with monasteries, castles and lots and lots of vineyards.  Doesn't get much better than this!