Upton House is a National Trust country house about 7 miles north-west of Banbury, just over the Warwickshire line. The house was remodelled in the 1920s for Lord Bearsted and is known for its art collection, period interiors, and terraced gardens.
It is not in Banbury itself, but it is close enough to be one of the town's best day-trip anchors. Combine it with Broughton Castle only if you have a car and both are open.