The Wavis Ravine was a ravine on Pakha.
In the 37th century, when Vor'r'na was possessed by the Diadem, he tried to escape to the Wavis Ravine. As the Third Doctor tried to take the Diadem away from him, Vor'r'na slipped and fell into the ravine. The Diadem was lost until 3985 when an expedition was sent out to find it.
Some Pakhar believed that the Ravine was bottomless. Others believed it led to the heart of Pakha, where the Dæmon Mianik'ha lived. (PROSE: Legacy)