If you look around, you will find tourist traps all over the world with names like Spook Hill, Magnet Hill, Gravity Hill, Antigravity Hill, Confusion Hill, Mystery Hill, Eerie Hill, Crazy Hill, etc., etc., etc.

What makes these hills worthy of tourist attention? Basically, the locals claim that the hill is “haunted” in such a way that things roll uphill. Well, things of course roll downhill, and that's all that happens on these hills too. What is going on in each case is that the local environment tends to suppress the true horizon and offer  false visual cues as regards to slope. To see how impressive this illusion of slope can be, here's a snapshot of a Japanese Spook Hill by Prof. Akiyoshi Kitaoka.

What we see in the photo is apparently a downslope leading to a narrow valley, followed by an upslope on the other side. And it looks this way to the naked eye. But what it actually is is an upslope, leading to an abrupt transition to a still greater upslope. In other words, we are looking up a hill in the photo, but it appears we are looking down one hill and then up another. See a more extended discussion here. Another discussion is here. And here is another discussion, with an embedded video.

Here are just a very few of such locations in the US and Canada. United States: Confusion Hill, Idlewild 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. A worldwide list of Spook Hills can be found here. And here is a good and clear description of a Gravity Hill that the tourists haven't discovered yet.

Winners of the 2008 Best Optical Illusions of the Year contest have been announced, and you can check them out here. I thought a surprising number of the winning entries were either weak or didn't work at all. My favorites were Ghostly Gaze, Rolling Eyes, Skyscrapers and Clouds, Pinball Wizard, Perpetual Collisions, and Naturally Interfering Shapes.