Gravity maps show the Earth's surface in color, where the various colors represent the difference between the measured gravity and the gravity predicted from a theoretical reference geoid. The whole Earth is, however, scattered with gravity anomalies.

It's worth pointing out that there is no such thing as an actual gravity spot, a place where gravity seems to work sideways or otherwise unexpectedly at least, not that a person would ever be able to detect. A person can sit in a chair halfway up the wall supported only by its back legs. Balls will seem to roll and water will seem to flow uphill. A person appears taller who stands under the low end of a tilted beam than a person who stands under the high end. Within these structures, any number of conventional optical illusions are constructed and can be performed. Like many similar attractions around the world, these mystery spots consist of crazily built wooden cabins built on sharp angles the range of 18 to 25 degrees off of level is common. We felt very light headed or top heavy, felt like something trying to force us right off the hill. There was no barbed wire fence near where we were at the time, and as far as we knew, no excessive mineral in this ground. We noted the compass to vary a small amount on the transit. The Mystery Spot in Santa Cruz, California says: The Native Americans called the area the 'Forbidden Ground', a place to be shunned. Their horses would not come into the affected area, so they wouldn't. The Oregon Vortex, goes way back to the time of the Native Americans. No matter how many times they tried to level their tripod, the plum-bob would always be drawn far to the east, even as the level was reading level. stumbled across an area of land where their surveying equipment didn't seem to work properly. The Saint Ignace Mystery Spot in Michigan says: Typically, commercial mystery spot attractions cobble together a fictional account of how their location was 'discovered'. What is it about our brains that wants to interpret things wrong? Let's point the skeptical eye at what mystery spots are, how they work, and most importantly, why they work. Some of these apparent gravitational anomalies occur naturally, and some of them are purpose-built as attractions, but everyone either loves them or hates them.

Without knowing it, I had stumbled upon the reason for the success of the many so-called 'mystery spots' around the world. But everyone has some reaction to it: wonder, anger, or a good laugh. Most people immediately see the gimmick and probably get a kick out of it, some have their minds blown by the apparent phenomenon, and judging by the comments, some derisively think it was a deliberate attempt to deceive. Someone sent it to Phil Plait and he posted it on his Bad Astronomy blog, and that's how I originally met Phil. Smart people began emailing me and asking if there was some magnetic phenomenon or a strong wind in the mine. Now, it was an obvious joke, and neither John nor I had any inkling that anybody might take it seriously or think it was real.

I called it a 'gravitational anomaly' and put it up on YouTube. I dropped a handful of gravel and it fell up to the ceiling.

Ancient plumb bob