The inscription on the tower means "Fort Isosaari". Finnish word "Isosaari" could be translated as "Big Island". The photo was made from the pier. The soviet jeep "UAZ" is seen. Big brother took care of little Finland. Inscription on the blue plate says: "put forward your identity card and pass!" The island is restricted military zone...
PS 2019: now it is open for public and could be visited summertime by water bus from Helsinki.