Oh, just remembered! There's a huge tower on one side of the Danube, which they call the 'DonauTour' in the donauzentrum. There's a revolving restaurant on the top of it. Go there, the view is superb. And if the weather's good, go to the 'Donau insel'...a little island in the Danube. There's lots to do there, including caoeing and going on those really cool trampolines where you can jump and flip etc.