Duke Humphrey's Library, the oldest reading room of the Bodleian Library in Oxford, was used for filming library scenes in Harry Potter and the Philosopher's Stone (2001), Harry Potter and the Chamber of Secrets (2002) & Harry Potter and the Goblet…
Hardwick Hall was used as the exterior of "Malfoy Manor" (with CGI supplements), and the interior entrance hall was used as the Death Eater headquarters in "Harry Potter and the Deathly Hallows: Part I."
Alnwick Castle is a castle and country house in Alnwick in the English county of Northumberland, and was used for exterior shots of Hogwarts in Harry Potter and the Philosopher's Stone and Harry Potter and the Chamber of Secrets