...by car and taxi.
There are many car rental firms, specially in Helsinki. If you plan to go see more northern Finland, car could be a nice option. There are no road tolls in Finland, but be careful when you are driving, there is always a chance of a moose on the loose. In Finland you have to drive always with your car lights on.
Taxis are a bit more expensive, depending of the city, time and of course how long is the journey. You don’t need to leave a tip. In city-centrum taxi lines may be really long (especially at weekends), so be prepared to wait.
Indietro: Moving by train
Avanti: Moving by plane