Porvoo is situated near the Helsinki-Vantaa airport.
There is a bus connection to Porvoo ten times a day taking about 50 minutes. Most of the connections include one change of bus, but not to worry - the first bus is an airport shuttle designed to help you get on the right bus going to Porvoo. Find the timetables at matkahuolto.fi
Rent a car and the drive to Porvoo is about half an hour.