Espoo is accessible year-round as part of the Helsinki metro area. Summer (June to August) is the most pleasant time: Nuuksio National Park is at its best for hiking and wild swimming, the outdoor events programme picks up, and the long days mean light until midnight in June. The April Jazz festival takes place in spring, and Espoo Ciné film festival is held in August.
Winter in Espoo is dark and cold, but the city continues to function normally as part of the Helsinki region. Nuuksio National Park offers cross-country skiing when there is snow. The Helsinki-Espoo metro is heated and comfortable. If you are visiting primarily for Aalto University's campus architecture, winter makes the brickwork and copper detailing more dramatic in the low-angle light.