Hi Karen, it's just outside Tetbury in Gloucestershire, it's the National Arboretum. It's a peaceful and soothing place, and really beautiful in autumn and again in spring when the bluebells are out. And at Xmas, they light up the trees and you can go on after dark walks in the freezing cold! They usually have mince pies, mulled wine, coffee etc for sale to defrost walkers afterwards! But seriously, it's worth a visit if you're in the area.
SM