Finland is a member of the Schengen area, so travelling to Finland from inside of the Schengen area is very easy.
From the Ministry of Foreign Affairs, you will find information on from which countries you will need a visa and travel documents approved by Finland, and much more: http://formin.finland.fi/public/default.aspx?nodeid=49153&contentlan=2&culture=en-US
Find out more about Finland here: http://www.visitfinland.fi/en/
The closest and most suitable airport is Helsinki-Vantaa Airport https://www.finavia.fi/en/helsinki-airport/
Importing an Airsoft gun to Finland does not require a separate permit, but may require a separate guncase depending on the airline. It is good to be in contact with your airline in advance and to reserve time at airports if the authorities want to check your game equipment. If you fly through other countries, make sure to check the laws of the countries about airsoft guns.
From the airport you can rent a car or travel by train to Hämeenlinna or Lahti, where you can rent a car and travel to the game site. Train tickets can only be booked up to 84 days before the trip, but the schedules are mostly the same year round.
You can also travel to Finland by boat. The main ports are Turku, Helsinki and Vaasa.
You can get to Hämeenlinna directly from Turku by only one train change.
In Helsinki you should use taxi or public transport (tram or bus) to get to the main railway station.
It is best to come by car from Vaasa.
When travelling by car, you need an European registration plate or a country tag.
If you are bringing a special vehicle, please check with the regulations/legislation concerning it.
Make sure your car is insured.
The Hämeenlinna train station is 1 hour drive away from the game area and Lahti train station is 50 minutes drive away.
The best way to get to the place is by renting a car in Hämeenlinna or Lahti. You can also ask ridesharing from another players.
Padasjoki is a municipality in Finland, which has got internatiol fame from the video "Experience nothing". Despite its small size, the scenic Padasjoki offers all the services you need from your stay. For more information on the Padasjoki area, visit Padasjoki municipality website.
About 10km from the game area you will find the following services.
Finnish august can be very warm even up to + 20 °C during the day but also cold days when temperatures are only about 15°C are possible. Cold nights were temperatures to drop from + 5 to + 10 °C, which is aggravated by fog and moisture. So book a warm sleeping bag and clothes for cold nights. Autumn average temperatures.
The sun starts to set after 21:30 and the darkness takes about an hour. The sun rises after 05.00. Therefore, you need to take at least a headlamp with you.
In august, heavy rains / thunderstorms may also occur in Finland during hot summers, which may take a few minutes to hours or then only occur in smaller rains. So take with you your rain equipment, just a rain cover may not be enough in wet woods.
For example, you can check the forecast from Forecas or Finnish meteorological institutes websites.