We visited Buscot Park (National Trust and family home of Lord Faringdon) one day in June.
The garden was spectacular, with a lovely walled garden with deep herbaceous borders, and from the top of the steps looking down you could see water features on the other side of the garden. There is also an Italian water garden designed in 1904 by Harold Peto which slopes away from the house to the lake.
Inside the house is the spectacular Faringdon collection of paintings by Rembrandt, Rubens, Reynolds etc and my personal favourite room contains the Legend of the Briar Rose by Burne Jones, wonderful paintings illustrating the story of the Sleeping Beauty in the music room. When Burne-Jones visited Buscot from nearby Kelmscott Manor, he designed a framework of carved and gilt wood for the paintings, and also painted connecting scenes so that you feel you have stepped into the Briar wood, and are surrounded by the spellbound sleepers.
There is a shop and tea room to complete the day, and Buscot village itself is worth a visit, and the nearby River Thames if you fancy a walk.
Do check Buscot Park opening hours before visiting, as they are open every other week-end in the summer, as well as part of the week.