This Quest is to visit the publicly accessible Downton Abbey filming locations. Most of the TV series and movie is shot at Highclere Castle (above) and in the studio; Ealing for TV, Shepperton for the movie. Other regular TV filming locations include the church, hospital, coffee shop and bistro which are filmed in Bampton (below); Yew Tree Farm which is filmed at Cogges Manor Farm; and Downton station which is Horsted Keynes station, belonging to the Bluebell Railway; Basildon Park doubles at the interior of Grantham Hall, and as the location for Lady Rose's coming out ball and marriage; West Wycombe House is Aunt Rosamund’s home in Belgrave Square.
Most of the location shots are one-offs. Lady Sybil and her chauffeur eloped to Swinbrook. Bates gets locked up in Lincoln Castle. Lady Rose gatecrashed the servants' party in Hoxton Hall. The 2012 Christmas special was filmed at Inveraray Castle, 2013 at Basildon Park, 2014 and 2015 at Alnwick Castle (the former while we were there!).
In the movie, the royal parade and chase scene were filmed at Lacock; Mr Bakewell's shop, Branson Motors and the Kings Arms were at the Beamish Open Air Museum; the police station and club were in Little Germany, Bradford; the exterior of Harewood House was at the real Harewood House, the interior was at Wentworth Woodhouse; the train departing for London was at Pickering Station.
Sadly, there are quite a few other filming locations that are not open to the public. Also, bear in mind that most of the country houses are closed over winter and at other times. It is best to check your destination is open before you leave.
Your reward for visiting all 17 locations is the title Downton Abbey Aficionado. There is an intermediate rank of Enthusiast for visiting 8 locations.