The best time to book a Hop-On Hop-Off Berlin sightseeing tour is May through September. The weather is pleasantly warm and ideal for sightseeing or leisurely strolling. However, you can expect thick crowds during the peak season and high airfare as well as accommodation options. Between January and March, the weather gets chilled with long nights, but it is the cheapest time to explore Berlin. If this does not sound appealing, you can opt for the late autumn months of October and November.