If you have an extra day in Helsinki, take a tour of the historic old town Tallinn, capital of Estonia.  Take the Linda Line Express ferry (http://www.lindaline.fi/en/) the one hour and forty minute ride south across the Gulf of Finland to Estonia.  Purchase tickets the day before at the ferry terminal or online for a discount.  The ferry leaves every two hours in the summer.  Seats are first come, first serve, so arrive early to obtain a window seat on the second level.  Food and drink are available onboard for a reasonable price.