of rider discomfort. Another notable difference is the absence of any lateral movements, causing some enthusiasts to not consider the rides to be fourth-dimension roller coasters due to the fact that all movement is restricted to a two-dimensional plane. Kirnu at Linnanmäki in Helsinki, Finland, opened for the 2007 season and was the first of its kind. Later that year Inferno opened at Terra Mitica in Spain with an identical compact layout. In 2009, Insane opened at Gröna Lund with a different track layout. In 2011, the first ZacSpin in the United States opened at Six Flags Magic Mountain as Green Lantern: First Flight, and was themed to the DC Comics superhero of the same name. It features the same layout as Insane. S&S Free Spin In late 2012, S&S Worldwide unveiled a new concept called Free Spin which features a similar ride to Intamin ZacSpin. Each vehicle features two seating rows, and each row rotates independently. Because the axis of rotation is at the center of mass of each guest, rider comfort is significantly improved. Like with ZacSpin, Seats spin freely, but during several track sections a system of magnets forces a controlled inversion. The first installation of a 4D Free Spin was Batman: The Ride at Six Flags Fiesta Texas in 2015. Intamin ZacSpin second generation In 2016, Intamin announced an updated version that like Free Spin also features a vehicle with two seating rows rotating independently, and an axis of rotation at the center of mass of each guest to improve rider comfort. Inversion ambiguity There is considerable debate within the roller coaster community as to whether or not the spinning of these coasters qualifies as an inversion for the purpose of records. Guinness World Records gave Eejanaika the record with 14 inversions. However, other more coaster-specific record bodies such as the Roller Coaster Database do not recognize this claim and instead count only track inversions, which gives the record of 14 to The Smiler. Installations See also Wing Coaster – a type of ride by Bolliger & Mabillard which features similar trains to the S&S/Arrow design References External links A list of fourth-dimension roller coasters at the Roller Coaster DataBase Types of roller coaster S&S – Sansei Technologies