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The Sheldonian Theatre, was built from 1664 to 1668 after a design by Christopher Wren for the University of Oxford. The building is named after Gilbert Sheldon, chancellor of the university at the time and the project's main financial backer. It is used for music concerts, lectures and university ceremonies.
The building is Grade I listed. Link
Wikipedia: Link

The second-oldest surviving university in the world and the oldest in the English-speaking world. Although its exact date of foundation is unclear, there is evidence of teaching as far back as 1096.

Most undergraduate teaching at Oxford is organised around weekly tutorials at self-governing colleges and halls, supported by classes, lectures and laboratory work organised by University faculties and departments, the university is spread around the city.

More details at Wikipedia Link
University website: Link

Grade I listed buildings and structures are of exceptional, even international importance. There are over 6,000 in the country. Only 2.5% of listed buildings are Grade I listed.
In Scotland the classification is Category A
Index: Link