Most cruises of Northern Europe are offered from April through September. These cruises can vary greatly in length and call at ports in a variety of countries. As temperatures are warmer in the region during the summer months, tourist traffic also increases. Visitors can avoid some of the crowds by traveling during the shoulder seasons in the spring (April and May) or fall (September). The temperatures are cooler, but still comfortable during these months and the number of people visiting the sites will be greatly reduced. A few sailings operate in the winter (October to December) when the weather is much colder.