The scene where Haymitch (Woody Harrelson) reads Plutarch's letter to Katniss (Jennifer Lawrence) was originally scripted to be Plutarch (Philip Seymour Hoffman) talking to Katniss in person. Unfortunately, Hoffman died before the scene was filmed.
The cast has said multiple times that the most challenging scene to shoot was the sewer scene. It took three weeks to shoot and was physically demanding, and it was hot on the set since they shot on-location in actual sewers.
The circular apartment complex with the toxic oil trap is an actual location. The Espaces Abraxas is in a suburb of Paris, France. The CGI team digitally removed the many trees in the courtyard but made a few alterations to the site.
Many of the Capitol scenes were shot in Paris and Berlin.