Greenfield Valley Heritage Park, Holywell. Greenfield Valley Heritage Park is a 70-acre country park in the United Kingdom. It is located in Greenfield, near the town of Holywell in North Wales. It is well known for its woodland, reservoirs, ancient monuments, rich industrial past and its factories which played a part in the Industrial Revolution. Lots to see and do here. There are woodland walks, old mills to see, mill ponds, water features, children’s play area, Basingwerk Abbey, Tea room and