The Divinity School is one room within the Bodleian Library, below Duke Humphrey’s Library. Construction began in 1427 and it lasted until 1488 when it became the University’s first purpose-built lecture hall. You'll recognize it as being used as the hospital in the first Harry Potter movie!
You can access the building either by purchasing a ticket for £2.50, or by doing a guided tour of the full library starting at £10. For the full tour, check out tickets here and book either the 30-minute tour or 60-minute tour.