Christ Church College
The famous Hogwarts main staircase and landing used in The Philosopher's Stone and The Chamber of Secrets:
And the Dining Hall was the inspiration for Hogwarts' Great Hall. Fun fact: they couldn't film the scenes in here because it could only fit three rows of tables, but they needed four because of the number of houses in the story:
The Divinity School
This intricate room built in 1448 was used as the Hogwarts infirmary in four films. It's also the place Professor McGonnagal taught students to dance in The Goblet of Fire:
