For first timers, we recommend a Danube River cruise. It offers an enjoyable “tasting menu” of many top cultural sites. Another option will be the Rhine River cruise, it features stunning scenery and dozens of castles.
For second or third-timers, try the Eastern Europe via a cruise along the Lower Danube. And for more experienced travellers seeking something, you might consider the Douro River in Portugal or the Volga River in Russia.