# Gravity hill > "Magnetic hill" and "Mystery hill" redirect here. For other uses, see [Magnetic Hill (disambiguation)](https://en.wikipedia.org/wiki/Magnetic_Hill_\(disambiguation\)) and [Mystery Hill (disambiguation)](https://en.wikipedia.org/wiki/Mystery_Hill). A **gravity hill**, also known as a **magnetic hill**, **mystery hill**, **mystery spot**, **gravity road**, or **anti-gravity hill**, is a place where the layout of the surrounding land produces an [illusion](https://en.wikipedia.org/wiki/Illusion), making a slight downhill slope appear to be an uphill slope. Thus, a car left out of gear will appear to be rolling uphill against [gravity](https://en.wikipedia.org/wiki/Gravity). Although the slope of gravity hills is an illusion, sites are often accompanied by claims that magnetic or supernatural forces are at work. The most important factor contributing to the illusion is a completely or mostly obstructed horizon. Without a horizon, it becomes difficult for a person to judge the slope of a surface, as a reliable reference point is missing, and misleading visual cues can adversely affect the sense of balance. Objects which one would normally assume to be more or less perpendicular to the ground, such as trees, may be leaning, offsetting the visual reference. A 2003 study looked into how the absence of a horizon can skew the perspective on gravity hills, by recreating a number of antigravity places in the lab to see how volunteers would react. In conclusion, researchers from the Universities of Padua and Pavia in Italy found that without a true horizon in sight, the human brain could be tricked by common landmarks such as trees and signs. The illusion is similar to the [Ames room](https://en.wikipedia.org/wiki/Ames_room), in which objects can also appear to roll against gravity. The opposite phenomenon—an uphill road that appears flat—is known in [bicycle racing](https://en.wikipedia.org/wiki/Cycle_sport) as a ["false flat"](https://en.wikipedia.org/wiki/Glossary_of_cycling#F). ## See also * [List of gravity hills](https://en.wikipedia.org/wiki/List_of_gravity_hills) * [The Crooked House](https://en.wikipedia.org/wiki/The_Crooked_House) – a pub (now demolished) with an internal gravity hill illusion. ## References ## External links --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.edisonscientific.com/paperqa/tests/stub_data/gravity_hill.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.