Where is it?

Let's go. If you are in Saint-Petersburg, you must take the bus number (I'm forgot which) and go to Helsinki city. If you are russian, you should get the finnish visa at first either you will find yourself in big troubles on finnish border.

When you arrive to the central bus station of the capital of Suomi, you'll need to go out from the bus and move to the ZW direction to the Market Square (20 min). Then you should buy the ticket to the ferry (20 FIM) and wait (usually 15-20 min). You can feed the local cormorants with especially reserved white bread while waiting. Finnish cormorants are very big and impudent and like the white bread very mach.

The ferry goes to the Sveaborg near to 15 min. Total: there is 7h40' from
S-Petersburg to Sveaborg (except finnish custom and russian border guard check-point).

Ferry ticket