It has sometimes happened that, long after an underground house has ceased to be occupied, new settlers of another race have built their houses directly above these concealed retreats, quite unaware of their existence. Thus, at Airlie in Forfarshire, a cottage was supposed to be haunted because oatcakes, baking on the hearthstone, occasionally disappeared from sight in a mysterious manner. It was thought proper to pull down the cottage altogether, and then it was accidentally found out that the hearthstone was the roof-stone of an underground house, into which the cake had fallen through a crevice. Nobody had thought of lifting the hearthstone before proceeding to the extremity of pulling down the house. That was in the eighteenth century.
Stories of the Mound- Dwellers' in The Celtic Review
David MacRitchie