A trip along the Austrian Danube unfolds like a treasured picture book. Roman ruins (some dating to Emperor Claudius), remains of medieval castles-in-air, and Baroque monasteries with "candle-snuffer" cupolas jut out from steep river banks; the river cuddles on its shores villages so cute they should get their cheeks pinched. Today, thanks to the technology of modern dams, travelers have the luxury of tamely observing this part of Austria from the deck of a comfortable river steamer. In good weather the lazy nine-hour trip upriver from Vienna to Linz is highly rewarding. If your schedule allows, continuing onward to Passau may be less dramatic but gives more time to take in the picturesque vineyards and the castles perched on crags overlooking the river.