This cache is on the Forest boundary, but has been set as a waypoint between Eastern Whittaburrow and Red Lake foot. 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.
When approaching from Eastern Whittaburrow, there is a fairly well-marked path along the ridge between the two burrows. From here, head west until you come across the old tramway, then turn north towards Red Lake spoil tip. At Crossways (waypoint below) turn onto the Two Moors Way, and head for the river crossing (waypoint below). The trail on the OS map leads to Red Lake Ford, but on the ground the path naturally takes you to this crossing.