From the article "Harry Potter Filming Locations in Britain" on Rick Steves' site:
(for those of you that might not know, Rick Steves is an American author and television personality focusing on European travel- he had a long running travel show on PBS).
Locations in Oxford:
Hogwarts, Harry’s prestigious wizarding prep school, is a composite
of several locations, many of them real places in Oxford.
Christ Church College inspired two film sets familiar to Potter fans.
In The Sorcerer’s Stone, the kids are ferried to Hogwarts and then
ascend a stone staircase that leads into the Great Hall. Christ
Church’s high-ceilinged dining hall was a model for the one seen
throughout the films (with the weightless candles and flaming
Christ Church College's dining hall
Hogwarts' Dining Hall:
Christ Church College, inspiration for the Great Hall:
Later in The Sorcerer’s Stone, Harry sneaks into the restricted book
section of Hogwarts Library under a cloak of invisibility. This scene
was filmed inside Oxford’s Duke Humfrey’s Library. Hermione reads
about the Sorcerer’s Stone here, too.
At the end of The Sorcerer’s Stone, Harry awakens in the Hogwarts
infirmary, filmed in the big-windowed Divinity School, on the ground
floor of the Bodleian Library; Ron also recuperates here after being
poisoned in The Half-Blood Prince. In The Goblet of Fire (2005),
Mad-Eye Moody turns Draco into a ferret in the New College cloister.
Locations in Durham and Northeast England
In The Sorcerer’s Stone, Harry walks with his white owl, Hedwig, through a snowy cloister courtyard located in Durham’s Cathedral.
Harry first learns to fly a broomstick on the green grass of Hogwarts’
school grounds, filmed inside the walls of Alnwick Castle, located 30
miles from Newcastle. In The Chamber of Secrets, this is where the
Weasleys’ flying car crashes into the Whomping Willow.
Locations in Scotland
Also in The Prisoner of Azkaban, Hogwarts Lake was filmed using Loch Shiel, Loch Eilt,
and Loch Morar near Fort William, and Hagrid skips stones across the
water at Loch Eilt. Steal Falls, a waterfall at the base of Ben Nevis,
is the locale for Harry’s battle with a dragon for the Triwizard
Tournament in The Goblet of Fire.
Locations in and around Bath
Many scenes showing the mysterious side of Hogwarts were filmed in
the elaborate, fan-vaulted corridors of the Gloucester Cathedral
cloisters, 50 miles north of Bath. In The Sorcerer’s Stone, when Harry
and Ron set out to save Hermione, they look down a long, dark
Gloucester hallway and spot a 20-foot troll at the far end.
In The Sorcerer’s Stone, the scene showing Harry being chosen for
Gryffindor’s Quidditch team was shot in the halls of the 13th-century
Lacock Abbey,13 miles east of Bath. Harry attends Professor Snape’s
class in one of the Abbey’s peeling-plaster rooms — appropriate to
Snape’s temperament. (You can visit with recommended Mad Max Tours.)
Outdoor scenes from the first Deathly Hallows, in which Harry, Ron,
and Hermione take refuge in the woods, were filmed in the Swinley
Forest area of Windsor’s Great Park.
Also, from wikipedia:
- Alnwick Castle, Northumberland (Hogwarts exterior)
- Bodleian Library, Oxford (Hogwarts interiors)
- Christ Church, Oxford (Hogwarts interiors)
- Durham Cathedral (Hogwarts interiors)
- Gloucester Cathedral (Hogwarts corridors)
- Harrow School, (Professor Flitwick's classroom)
- Lacock Abbey, Wiltshire (Hogwarts interiors)
- New College, Oxford (Hogwarts cloisters)
- St Paul's Cathedral, London (Spiral staircase in Hogwarts)