This cache is not on the ancient Forest boundary of the 1240 Perambulation, but has been placed as a waymark between North and South Hessary Tors. 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.
The Forest boundary does has never passed through Princetown, but some way to the west, on a straight line between the Hessary Tors. The line of bound stones between the tors can be followed if you want to stick to the boundary line, but the walking is much easier if you detour through Princetown.
If doing this cache as a standalone, there is parking at the nearby High Moor Visitor Centre. If doing the Perambulation as a route, the next point on is North Hessary Tor. Follow the path that this cache lies at the start of until it meets the road by the brewery. Turn left and head to the five bar gate onto the moor.
Please rehide the cache carefully.