Razor Rubble

Source: Paizo Blog

Either rubble made of sharp stone, or laced with small sharp blades, this terrain functions like difficult terrain, but each square a creature enters deals 1 point of damage to that creature. A creature moving at half speed, or that succeeds at a DC 15 Acrobatics check as a free action when first moving into an area of razor rubble can avoid the damaging affects for the round but not the difficult terrain effect.