Passage: Development of Thor: The Dark World began in April 2011, when producer Kevin Feige announced plans for a sequel to follow the crossover film The Avengers. In July 2011, Kenneth Branagh, the director of Thor, withdrew from the project. Brian Kirk and Patty Jenkins were considered to direct the film before Taylor was hired in January 2012. The supporting cast filled out in August 2012, with the hiring of Eccleston and Akinnuoye-Agbaje. Principal photography began in September 2012 in Surrey, England with filming continuing in Iceland and London, before wrapping up in December 2012. Thor: The Dark World was converted to 3D in post-production.

Question: What month did they start shooting?
September