Gravity Hills, or "Magnetic Hills", "Mystery Spots", are found all over the world: they are places that appear to be a hill with an upward slope, but when you put your car in neutral (or roll a ball on the street, for that matter), the car (or ball) seemingly rolls up the hill.

There are usually ghost stories accompanying these oddities. The most prominent is this:
"A busload of children (or car full of teenagers, or distraught woman walking carelessly in and out of traffic) was hit by a train (or semi truck, or abusive husband driving dangerously and looking for his wife) at or near the hill. The restless spirits of the school children (or teenagers, or now dead distraught woman) will push your stalled vehicle up the hill and out of harm's way, so you do not meet the same fate. Usually there is a nice embellishment thrown in at the end, often including several little hand prints that appear on the steamed up back window or dirty bumper (or a terrifying reenactment of the horrible accident, complete with old-timey automobiles and crunching metal and glass, or a glimpse of the dead scorned woman). Often, there are also reports of spooklight (balls of light that float and zig zag) activity on these "supernatural" hills.

   Usually Gravity Hills can be explained rationally by this fact: the road may appear to be on an incline, but the surrounding landscape creates an optical illusion, and the road is actually going slightly downhill. Surveyors have tested some of these places and found this to be true.

This is a Gravity Hill (or in this case, 'magic hill') near Dundalk, Ireland.
 

here are a few other sites about this phenomena:
http://paranormal.about.com/library/weekly/aa120301a.htm
http://www.roadsideamerica.com/set/SCIspots.html
http://www.gravityhill.com/