You're looking for the Pound or Pinfold just west of the pub. It was restored in 1992 and has a Millennium monument within. There's a mossy bench, and a source of water in the corner for those held within. If you don't know about Pinfolds or Pounds, follow the GPS and a handy sign on the gate will tell you all about them.
Parking right next to it by the Sun Inn and phone box. Kneeling down would help. Please be gentle with the surroundings and re-hide well - don't drop it!