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We recommend either the I-train or Finnair City Bus (both take 30-35 min). For all alternatives, see: http://www.finavia.fi/en/helsinki-airport/to-and-from/train-buses-and-taxis/. Note that the If you take a train from the airport to central railway station, you can use the same ticket for a bus from Kamppi bus station to CSC (regional ticket 5.50 EUR, valid for 80 minutes). The Finnair City Bus ticket is not valid to valid in other buses, but the train ticket is.
Helsinki to Venue (Espoo)
Busses Buses 102 (platform 41) and 103 (platform 42) from Kamppi bus station (Buses to Espoo), exit stop Miestenmetsä. (102T and 103T also go to CSC, but take a longer route.)
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