You can easily reach the planetarium from Turku on a bus by purchasing a ticket to the bus stop of Tuorla. Distance from the bus stop is a bit more than 500 metres. You can drive all the way to the planetarium with your own car. The address for a navigator is "Väisäläntie 20, Piikkiö". If you come from the direction of Helsinki, Tuorla can be found just after Raadelma area.
Using the accompanying 3D map you can navigate in Tuorla area. When you turn off road 110 you will find Hostel Tuorla ahead on the left after just 50 metres. When you turn left there, another 400 metres take you to Tuorla Observatory buildings and a further 100 metres to the planetarium (the large blue building at the side of the observatory hill).