Much earlier in the year we went to Frogmore House.
I can't remember too much about it so have had to resort to good old Wikipedia (sorry!):
Frogmore House is a 17th-century English country house owned by the Crown Estate. The house is situated within the Frogmore Estate, which is itself located within the grounds of the Home Park, Windsor, Berkshire. Half a mile south of Windsor Castle, Frogmore was let to a number of tenants until the late 18th century, when it was used intermittently as a residence for several members of the royal family.