Tourist season does not get into full swing until the summer months of June through September, leaving May to be slightly less crowded. Granted, you won't be the only person there, but compared with August, places like Prague will feel less like a theme park and more of the cultural center it is known for.
In Europe, May is often one of the best months of the years, filled with mild temperatures, little rain, and plenty of blue skies and sunshine. For example, Prague's average temperatures range from 46 to 64 degrees Fahrenheit with an average of 2.4 inches of rain, considerably less than June, July and August. Warsaw, Poland, and Budapest, Hungary, experience similar temperatures and rain averages.
Many times, prices for accommodations vary by season, with the summer and Christmastime having the highest prices and the rest of the year considered the off-season. Most hotels, pensions and hostels consider May to be part of the off-season. Not only will the price be cheaper, but the establishment will also be less crowded, making for a more affordable and comfortable stay.
May often is considered an off-season month with airline companies as well, international and intra-European. By arriving and departing before the beginning of June, you can save a considerable amount of money that can otherwise be spent on something better and more worthwhile. As always, purchase your tickets at least two weeks in advance to save even more money.
Many European cities have public parks. During the month of May these parks come back to life. The flowers bloom, the leaves grow, and the local people reappear. Sitting in a European park on a nice spring day offers some of the most relaxing times and best opportunities to watch people, ride a bike and lie in the sun.
Visitors are often surprised at the amount of open space left in Europe. Unlike the United States, suburban-sprawl did not take over, leaving endless amounts of unspoiled countryside sometimes immediately outside of a major city's boundaries. In May, the rolling hills, mountains and forests turn green, offering plenty of opportunities to hike and bike as well as get to know the local culture in the numerous small villages that dot the landscape.