A ferry to the Suomenlinna fortress island runs about twice an hour, depending on the time of day, and costs €2 one-way and €3.80 round-trip. Ten-trip tickets issued for city public transport can be used on the ferry, too. From June to August, private water buses run from Kauppatori to Suomenlinna, charging €3.50 one-way and €5.50 round-trip.
Suomenlinna Ferry. Suomenlinnan Liikenne Oy, Merikasarminkatu 10, Helsinki, Uusimaa, 00160. 9/3102–1000; www.slloy.fi.