Two weeks before location shooting was scheduled to begin for Monty Python and the Holy Grail, the Scottish Department of the Environment withdrew permission for the Pythons to shoot within their castles, saying that the film’s script would be “incompatible with the history and fabric” of the castles. The interiors of Camelot (where ‘Knights of the Round Table’ takes place) and Swamp Castle, and exteriors of Castle Anthrax, French Castle and the opening castle were all shot at Doune Castle (with various rooms redecorated and reused many times).
Recently-rebuilt Castle Stalker was used for the Castle Aarrgg. Both of these were privately owned and could be used. The Constitutional Peasants’ castle and Camelot are each 10ft high plywood model which had a tendency to blow over in the middle of each take; hence the trailer shows another in-joke, with King Arthur knighting someone who just built a large castle but when the plywood building falls over Arthur stabs him. –IMDB
In 2005, the movie was adapted into a musical comedy, Monty Python’s Spamalot, and won the Tony award for Best Musical that year. It starred Tim Curry (as King Arthur), David Hyde Pierce, and Hank Azaria. One of the musical’s creators, Eric Idle, explained the title: “It comes from a line in the movie which goes: “we eat ham, and jam, and Spam a lot.”