Southern Finland is divided into six regions.
Southern Finland is the most densely populated region of Finland, but it still manages to provide easy access to areas of great natural beauty. There are a number of excellent National Parks, such as Repovesi and Valkmusa in the Kymenlaakso region and Nuuksio and Sipoonkorpi near Helsinki. The region extends from close to the Russian border in the east to Uusikaupunki on the coast of the Gulf of Bothnia, and includes the inland towns of Kouvola, Lahti and Hämeenlinna, and the coastal towns of Kotka and Porvoo.
All international and domestic flights land at the compact, modern and airy Helsinki-Vantaa International Airport, which is located in Vantaa, 18 kilometers to the north of the central Helsinki. Note that in recent years the airport has become crowded, so expect delays when going through security, particularly during the Scandinavian summer holiday period. There are two adjacent terminals, connected by a short walkway:
T1: SAS, Blue1 and other Star Alliance airlines (except Turkish Airlines in T2). T2: Finnair, OneWorld partners, KLM, Norwegian and most other airlines.
Long-distance national and international buses terminate at the new underground Central Bus Station (Linja-autoasema) in the Kamppi Center (Kampin Keskus). The station is adjacent to Mannerheimintie, directly connected to the Kamppi metro station and within a short walking distance from the Central Railway Station.
Low-cost bus operator Onnibus operates many lines and are rapidly expanding their connection network. Check latest information on connections from their website. Prices start from as low as 3 EUR (if booked in advance). Onnibus buses to Tampere leave from the small curbside stop in front of the Kiasma art museum and the ones to Turku depart from the Kamppi long-distance bus terminal.
For travel from St. Petersburg (Russia), Russian minibuses depart from the Oktyabrskaya Hotel (opp Moskovsky train station) around 10PM and arrive behind Tennispalatsi at Eteläinen Rautatiekatu 8, one block away from Kamppi, early in the morning. Departures back start around 10AM in the morning. Other minibuses are parked along Fredrikinkatu, with the departure time and price often posted on them. The trip costs around 15 euros, making this by far the cheapest option, but the buses are cramped and uncomfortable and some of them stop at numerous supermarkets on the way so that Russian passengers can go for tax-free shopping. Do not expect drivers to speak anything but Russian. The border crossing time might be substantially longer than with regular buses.
All long-distance trains throughout Finland and the Russian cities of Moscow and Saint Petersburg terminate in the heart of the city at the Central Railway Station]. This station also provides easy interchange to the metro and tram lines. All the trains also stop at Pasila station, which is the last station before Central Railway Station. From Pasila you can change to tram and bus lines
Copterline runs a fairly expensive Tallinn-Helsinki service, taking around 18 minutes. This is the world's fastest capital-to-capital city transfer. (The service was discontinued, but is told to continue August 2013).
Between cities and major towns you can use the trains  or buses . Hitchhiking is uncommon but possible, but be aware that some roads have very little traffic. If you chose smaller country roads, cycling is a possibility and you can camp wild as long as you regard the "joka miehen oikeudet", which states basically "behave".
In Helsinki Metropolitan area there's well-functioning public transport system HSL. Helsinki, Espoo, Kauniainen, Vantaa, Kerava, Sipoo and Kirkkonummi form an integrated regional public transport area where traveling is easy and affordable. You can travel with a Travel Card which can be used on all public transport within the entire region. HSL also provides mobile services that make traveling easier.