It is in Finland, on the northern shore of the Gulf of Finland, Svartholm fortress protects the sea route to the town of Loviisa.
There is a not a long ride from Helsinki or St. Petersburg by bus to Loviisa, and than by the foot from the bus station in Loviisa to the south by the church and the market square to the pier for 10-15 minutes...
The motorboat goes 3-5-6 times a day to Svartholm in summertime, (5 euros - cash / Visa / Mastercard) and within 15-20 min you will get to the fortress.