It's at an area called Pen-y-Dinas, above Happy Valley Merddin. At Pen y Dinas, hidden in the dense undergrowth are an indeterminate number of stone circles, and the defensive slopes of an ancient British hill fort.
From Eve Parry's Mysterious Mountain book:
On the Southern slopes of the Orme, overlooking the town of Llandudno, there is an area known as Pen Dinas, where are the remains of a prehistoric settlement. Close by, on the edge of a precipice, lies a large rectangular stone. It is known as the Rocking Stone and a metal plaque may be seen attached to the stone, to this effect. Legend tells us that the Druids used the Rocking Stone as a means of proving the guilt or innocence of criminals. The poor, trembling creature was made to stand on the stone. If the accused was able to make it rock, they were deemed to be innocent, but if the stone stood firm, the guilty wretch was thrown over the cliff to be broken on the rocks below. There are many sources for this story, some saying that the stone still rocks and others insisting that it will not move. Could it be that the stone still possesses the power to judge guilt or innocence?
