From Helsinki-Vantaa Airport (distance 20 km): Take Finnair City Bus (http://media.finnair.com/files/pdf/FINNAIR_CITY_BUS_TIMETABLE.pdf) and get off the bus at the stop “Hesperian puisto – Hesperiaparken” which is just after passing Scandic Continental Helsinki.
From Helsinki train station (distance 2 km): Walk to Mannerheimintie and take for example Tram 10 or 4 and get off the tram at the stop “Hesperian puisto”. You can check the route in Journey Planner (http://www.reittiopas.fi/en/).
Helsinki City Official Tourism Website :
http://www.visithelsinki.fi/In_English/Visitor/Helsinki/Welcome_to_Helsinki!.iw3