This cache is not on the ancient Forest boundary of the 1240 Perambulation, but has been placed as a waymark between Soussons Down and Riddon Ridge. More details about the Perambulation can be found on the cache page for the Dartmoor Forest Bonus. On the front page of the logbook is an adjustment to be made to the Bonus co-ordinates, which you will need to find the Bonus.
If doing this cache as a standalone, there is parking nearby (waypoint below). If doing the Perambulation as a route, the next point on is Riddon Ridge. From this cache at Cator Common, continue down to the gate and follow the road across the brook once more. Continue up the road until you come to a large grassy track (waypoint below). This track will lead you all the way to Babeny Farm, and although wet, is the easiest route across Riddon Ridge.