Public transportation to Tangosauna
From Helsinki Vantaa Airport to the Marathon venue
If you can't make it for the Tangosauna bus, you can either travel by train+train+bus or bus/bus+6km taxi. The national route planner https://opas.matka.fi/ has an updated schedule, use "Terminal 2 Saapuvat / Arrivals, Vantaa" as departure and "Vierumäki Country Club" as destination. Here is a route suggestion.
Travel to Tangosauna with train+bus:
At the airport, board a train to Tikkurila (direction Pasila/Helsinki)
At Tikkurila Railway station, board a train to Lahti
At Lahti Railway station, find the bus stop named A (ask for directions there, if unsure)
At platform A, Board bus 88 (direction Heinola) or 89 (Direction Valkjärventie), they depart at least at 15:18, 16:18, 17:18, 18:18, 18:48, 19:18, 19.48, 20:18, 22:18, 22:48 and 23:18. Note: If you arrive Tangosauna after 17:00, you should check in at Scandic Hotel Vierumäki - right next to the bus stop.
Go off at the stop named Rampsintie. Here you can check in to your room at Scandic Vierumäki Hotel and finish off with a short walk to Tangosauna.
Example journey: You land at 17:00. You catch the 17:33 P-train from the Airport (Direction Pasila/Helsinki), it arrives in Tikkurila at 17:39 - from there you catch the 17:48 Z-train to Lahti. Arrival at Lahti railway station is 18:38, where you find your way to Bus 89 (platform A). After jumping off the bus at the Rampsintie stop, you can check in at Scandic Hotel Vierumäki before walking over to the country club.
Example journey 2: You arrive too late to catch the 88 or 89 bus from lahti (after 21:00). You find the stop for long distance bus travel at the airport, and at 22:30 board the Savonlinja bus headed to "Mikkeli matkakeskus". You go off at "Vierumäen liittymä" (the bus driver will help you). There is a gas station here, where you get some snacks and ask the staff to order you a taxi. Take the taxi to Scandic Hotel Vierumäki where you check in and finally you walk to the Country Club.
From Marathon venue to Helsinki Vantaa Airport
Travel time: about 2 hours 30 minutes.
Take the bus 89 (direction Orimattila Linja-autoasema) from Rampsintie (Departure times: 08:34, 09:34, 10:34, 11:34, 12:34, 13:34, 14:34, 15:34, 16:34, 17:34, 18:34, 22:34). It should arrive in Lahti travel center after 40 minutes where you can catch a train towards Tikkurila and then switch to the train to the airport. Total travel time is between 2h 20 minutes and 3 hours depending on your connections.
Example journey: You need to be at the airport at 14:45. You check the VR railway company's website, and see that you can be at "Helsinki Airport" by 14:45 if you hop on a train leaving Lahti at 13:20 with one change at Tikkurila station. To catch that train, you can take the bus (schedule above) from the venue (a few hundred meters walk) at 12:34, so you’ll have time to have breakfast and maybe even dance a couple of tandas before you go (just make sure that you know exactly where the bus stop is - ask the staff at the venue).
Link to route planner