Psychological Science, 14, 441‐449 (2003) Antigravity hills are visual illusions Paola Bressan, 1 Luigi Garlaschelli, 2 and Monica Barracano 1 1 Università di Padova, Padova, Italy and 2 Università di Pavia, Pavia, Italy Antigravity hills, also known as spook hills or magnetic hills, are natural places where cars put into neutral are seen to move uphill on a slightly sloping road, apparently defying the law of gravity. We show that these effects, popularly attributed to gravitational anomalies, are in fact visual illusions. We recreated all the known types of anti‐gravity spots in our laboratory using tabletop models; the number of visible stretches of road, their slant, and the height of the visible horizon were systematically varied in four experiments. We conclude that these effects follow from a misperception of the eye level relative to gravity, caused by the presence of contextual inclines or a false horizon line. Address correspondence to Paola Bressan, Dipartimento di Psicologia Generale, Università di Padova, Via Venezia 8, 35131 Padova, Italy; e‐mail: paola.bressan@unipd.it. Antigravity hills (also known as gravity hills, spook hills, or magnetic hills) are natural places where cars put into neutral are seen to move uphill on a slightly sloping road, apparently defying the law of gravity. Typically, the “spooky” stretch of road is rather short (50–90 m), only a few meters wide, and surrounded by a natural hill landscape, without nearby buildings. Such places are found in several countries all around the world, 1 and have been tourist attractions for decades. They should not be confused with the “mystery spots” found in amusement parks. These are generally tilted cabins, purposely built as such; a person walking inside feels disoriented, getting a very strong impression of standing at an angle in a perfectly normal room (Gregory, 1998; Shimamura & Prinzmetal, 1999). The effects experienced on spook hills are so impressive that people account for them by appealing to physical (magnetic or gravitational) anomalies; these are indeed the only explanations offered to the tourists on site. Magnetic causes can be ruled out easily, because the effects are visible even on nonmagnetic materials, such as plastic balls or water poured on the ground. The other favorite explanation is that in these locations the force of gravity is 1 We are aware of antigravity hills at the following locations. United States: Confusion Hill , Idelwild Park, Ligonier, Pennsylvania; Gravity Hill , northwest Baltimore County, Maryland; Gravity Hill , State Route 42, Mooresville, Indiana; Gravity Hill , State Route 96, south of New Paris, Bedford County, Pennsylvania; Gravity Hill , White’s Hill, Rennick Road, La Fayette County, Wisconsin; Gravity Road , Ewing Road, Route 208, Franklin Lakes, Washington; Mystery Hill , Highway 321, Blowing Rock, North Carolina; Mystery Spot , Putney Road, Benzie County, Michigan; Spook Hill , North Wales Drive, North Avenue, Lake Wales, Florida; Spook Hill , Gapland Road, Burkittsville, Frederick County, Maryland. Canada: Gravity Hill , McKee Road, Ledgeview Golf Course, Abbotsford, British Columbia; Magnetic Hill , Neepawa, Manitoba; Magnetic Mountain , Canada Highway, Moncton, New Brunswick. Europe: Ariccia , Rome, Italy; Electric Brae , A719, Croy Bay, Ayr, Ayeshire, Scotland; Malveira da Serra , Road N247, Lisbon, Portugal; Martina Franca , Taranto, Italy; Montagnaga , Trento, Italy; Mount Penteli , Mount Penteli, Athens, Greece. Other countries: Anti‐Gravity Hill , Straws Lane Road, Wood‐End, Victoria, Australia; Morgan Lewis Hill , St. Andrew, Barbados; Mount Halla , Cheju Do Island, South Korea.