Broadway Tower, Cotswolds
Broadway Tower is a folly built on the ridgetop of the Cotswold escarpment (OS grid reference SP114362, ) at the close of the eighteenth century by the Earl of Coventry. It is privately owned, but open to the public.
Following the ridgetop a few kilometres north is another fine viewpoint (or at least it should be, if I can ever visit on a nice day!), Dover's Hill (OS grid reference SP137397, ) above the village of Chipping Campden:
If you head a bit further North-East you should find Hidcote Manor Garden, yet another interesting National Trust property I've visited.