From the Old Severn Bridge:
Leave the M48 at junction 2, (The first one after the bridge.) Head for Chepstow. Take the first turning left off the Chepstow roundabout (A48-Newport).
Stay on the A48 all the way. Do not take the Caldicot exit off the small roundabout after the big hill. Keep heading for Newport all the way until you get to Caerwent. There is a big brown sign with "golf course and gardens" on it.
Turn left into Caerwent, then turn left at the crossroads where you see the Brown Tourist Flower.
Continue out of the village and where the road bears sharply left, turn right as directed by the Brown Tourist Flower.
Over the brow of the hill, past the golf club on your right and follow the road over the brow of the hill, under the wooden road bridge then bear round to the left and Dewstow House is on your left.