Once the home of Lord Castlereagh, this 18th-century house sits on the eastern shore of Strangford Lough. Its lush gardens were named one of the 10 best in the world by Britain’s Daily Telegraph newspaper in 2014, and are a candidate for UNESCO World Heritage status. An impressive array of unusual plants flourish here, due to a rare mild microclimate—the gardens almost never experience bad frosts. Inside the house, the excellent art collection includes the Hambletonian by George Stubbs and family portraits by Pompeo Batoni and Anton Raphael Mengs. The Temple of the Winds, a fine 18th-century banqueting house, is also on the estate, but it’s only open on Sunday afternoons (and not in winter). Admission to the house is by guided tour only.