On a day trip from Vienna I went to both Krems, Weißenkirchen and Dürnstein. Both proved to be quite a pleasant surprise.

Krems is the central town of the Wachau and has a nice historic town with a monastery to be visited. Some modern museums are nearby, notably a very good caricature museum. From Krems you can take the Wachau Train which goes along the left Danube bank through the Wachau villages. Weißenkirchen is the first stop. It is the village displaying the oldest architecture. It is very picturesque with its enormous medieval fortified church in the middle of the village. Dürnstein (the next stop of the train) is probably the prettiest of the three and is overloaded with tourists on weekends. It is beautifully located along one of the Danube's curves, amongst vineyards and near the ruins of Dürnstein Castle. Its most spectacular views are from the local Jesuit monastery that can and should be visited exactly for this reason.

The Wachau is very compact and easily accessibly with public transport from Vienna. Note that there are no bridges so if you want to visit famous Stift Melk you have to take a different train from Vienna or go all the way to Sankt Pölkten. Famous local products are wines and apricot jam.