As an university town Oxford is about the academics. While the university itself boasts gorgeous gothic architecture, the main appeal is its significance in literature. Oxford was once home to J.R.R. Tolkein and C.S. Lewis, among many other British writers. A stop at the Eagle and Child allows you to have a pint where they did. Be careful though, this place can get crowded very quickly. The Bodleian Library will occasionally have special exhibitions for their, and others works so always check the schedule before you travel. A bus trip away is also C.S. Lewis' home, where he was first inspired to write about Narnia.
Also a bus ride away is Blenheim Palace, one of England's largest houses. You can spend the entire day wandering the grounds, which includes two impressive lakes and forest walks. For a bit of history you can explore the palace itself, the birthplace and former home of Winston Churchill.