Europe's weather varies from region to region, but for the most part the continent has cool summers and cold winters. The summer months (June, July and August) are regarded as Europe's peak tourist season. Temperatures are warmer for sightseeing, and outdoor activities, such as hiking, biking and sunbathing, are popular. Keep in mind, though, that summer is also the busiest time of the year for tourism in Europe, affecting prices and availability.
In Northern Europe, where the climate is naturally cooler and winters are longer, the cruise season is short, generally running from April through September. You'll find a vast selection of cruises all summer long, ranging from short three-night sailings to longer voyages of 28 nights. If you don't mind the cooler temperatures, the fringe months of April and September see fewer tourists, and cruise prices may be slightly lower.
On the other hand, Mediterranean sailings operate year-round, but you'll have more options available from April through October. The busiest travel months for this region are July and August, when tourists are most likely to travel and the weather is sunny and warm. The average Mediterranean sailing is seven to 14 nights in length and departs from beautiful European cities like Rome, Barcelona and Athens.
In an effort to avoid large crowds, and possibly find a discount, consider traveling during the shoulder seasons in the spring (April and May) or fall (September). Temperatures are cooler, but tourist traffic is significantly reduced. A few sailings operate in the winter (October to December), when the weather is much colder. Something else to consider is that many Europeans take vacation during the month of August, so some smaller shops and businesses may be closed.