Kirnu (Finnish for "churn") is an Intamin ZacSpin roller coaster located at Linnanmäki in Helsinki, Uusimaa, Finland. It was manufactured by Intamin AG and on-site construction was handled by RCS GmbH.
The ride is the first "Ball Coaster" produced by Intamin. It is located between the Vekkula (funhouse) and Linnanmäki's performance stage.
The ride has a short layout, with no lateral turns. The cars spin, and the amount of spinning is affected by rider's weight.
The cars seat a total of 8 riders. 4 on each side of the track, with half facing forwards and the other half facing backwards. The 4 seats on each side of the track rotate independently from the opposite side.