Well, that's our name for it. It's a stretch of backcountry road (near the village of Siran) about 100 meters long that has a decidedly "X-Files" feel to it. Your car behaves in a really weird manner if you do this:
Result? The car starts to roll along the flat level road on its own. It gathers enough speed to roll UP the bend at the other end, finally coming to rest about 10 meters UP the hill. Look along the road and at the surrounding country and you'll notice the road looks level, but the country around you is sloping at a strange angle.
(When I last visited in September 2004 the illusion wasn't so strong - the local community council had resurfaced the road sometime before and broke the angle of the road. It's still worth a visit if you haven't seen one of these before.)
You could do this, for example, on a tour to the little walled city of Minerve in the Canyon de la Cesse for lunch, taking in Abbey Fontfroide in the afternoon.