We're located down a fairly remote country lane, so we will send you some precise directions when you book. But suffice to say you will need a car or taxi to travel to Hartwell.
If any of your party want to arrive by rail, you can pick them up at either Gunnislake Station (10 minutes drive away) or from Exeter or Plymouth (both about 45 minutes away). Alternatively, Tavistock bus station, with links to Plymouth etc, is just 12 minutes drive away.
The nearest airports are either Exeter (50 miles) or Newquay Cornwall (44 miles).