Gotland has a notably mild and sunny climate for its latitude — it receives more hours of sunshine than almost anywhere else in Sweden and is considerably drier than the mainland. The island can be visited year-round, but the seasons shape the experience dramatically.
July and August are peak season. The medieval week in early August (Medeltidsveckan) fills Visby with costumed Hanseatic merchants, jousting, and archery — it is the biggest event of the year and books out months in advance. The weather is reliably warm, the beaches are busy, and restaurants require reservations. Almedalen Week in late June brings Sweden's entire political class to Visby for a week of outdoor debate and events.
May, June, and September offer good weather with fewer crowds and lower prices. September is particularly recommended: the summer visitors are gone, the restaurant quality remains high, and the limestone meadows have their second flush of wildflowers.
Winter is quiet and cold, with many restaurants and attractions closed. Visby has a Christmas market that attracts visitors from the mainland, and the atmosphere of the empty walled city in snow is something quite different from the summer rush.