A Double Cone

The cone collocated on two inclined rails doesn't want to roll down. Instead if we leave it on the basis of the rails, it will roll to the top by itself.

In reality, during the motion to the top, the cone advances in the direction where the rails diverge, leaning on its always thinner part. By an appropriate choice of the rails' aperture angle and of the cone's angle, we obtain the motion of the centre of mass and the apparent paradox disappear.

A similar case are those "miraculous" roads where cars ascend without engines. If we look carefully at the slope, we realize that it's just an illusion.