If you sail in at night, it will be hard to ignore the eerily lit Durnstein Castle, (also known as Kuenringer Castle), which overlooks the small town named after it. Durnstein, in Lower Austria, is a port often visited on cruises to Austria. From there, it's a short 10-minute drive into nearby Krems, which is a popular wine-growing region in the Wachau Valley. By car, Durnstein is about an hour outside of Vienna.
Durnstein (meaning dry stone, because it's up so high) Castle is an undeniable draw for tourists, first mentioned in the 12th century as the location where Richard the Lionheart of England was held captive by Leopold V during the Third Crusade. It's a somewhat strenuous climb entirely uphill to the top, but most find that the views of the Danube and the town below are well worth the hike. A stretch of cobblestone street doubles as a pedestrian walkway through the quaint shops and eateries of the town (home to just more than 800 residents).
If your cruise line offers an optional excursion to a vineyard in Krems, be prepared to sample some fabulous white wines, as Austria is known for its award-winning Riesling and other varietals. Krems is also known for being the primary producer of Marillenschnaps, an apricot brandy. If you're interested in touring the city but don't imbibe, there's plenty to see. Krems is about 27 times larger than Durnstein, and it offers plenty of medieval architecture, including Steiner Tor, a gate erected in 1480.