Mount Stewart is a 19th-century house and garden in County Down, Northern Ireland, owned by the National Trust. Situated on the east shore of Strangford Lough, a few miles outside the town of Newtownards and near Greyabbey, it was the Irish seat of the Stewart family, Marquesses of Londonderry. Prominently associated with the 2nd Marguess, Robert Stewart, Viscount Castlereagh, Britain's Foreign Secretary at the Congress of Vienna and with the 7th Marquess, Charles Vane-Tempest-Stewart, the former Air Minister who at Mount Stewart attempted private diplomacy with Hitler's Germany, the house and its contents reflect the history of the family's leading role in social and political life in Britain and Ireland.