Rattle Hole is a pothole on moorland, with a single shaft descending 36m to a boulder floor from which a ledge gives access to a further pitch, about 25m deep, leading to a another gravel floor. There is a draught blowing through the boulder floor of the main pitch, suggesting open passages below, but digging has so far failed to find an extension. Dye testing has proved that water entering here emerges at Carrickbeg.
Rattle Hole highlights a persistent problem of the karst features of this area - the dumping of dangerous refuse, in this case the carcasses of fallen stock. This poses another serious health hazard to add to the many already identified for the Reyfad system.