Sea
Helsinki has boat connections with Germany, Poland, Russia, Sweden, Latvia and Estonia.
You can also arrive by boat via Vaasa (from Umeå, Sweden), Turku (from Stockholm, Sweden) and Hanko (from Nynäshamn, Sweden).
Addition to boat, you can use a ferry port at Hanko, Helsinki, Turku, Vuosaari, Naantali or Vaasa.
The fastest ferry crossing to Finland is via the Tallinn to Helsinki route, with a crossing time of approximately 2h.