Drewry explains in his notes for that dance that:  
The Bullers of Buchan are a rock formation in the cliffs north of Cruden Bay, Aberdeenshire. The most impressive feature is "The Pot" - a circular basin surrounded by tremendous rocks and with a narrow cave-like opening through which the sea flows into the cauldron. It is possible to enter the pot by rowing boat.  
Dr Johnson and Boswell visited the Bullers in 1773.  