Oxford's oldest building, the Saxon tower of St Michael at the North Gate dates from around 1040 AD — predating the university by two centuries. But for Reformation pilgrims, its greatest significance lies in what it once stood beside: the Bocardo Prison, a medieval gaol built into the city's North Gate watchtower. In 1554, Archbishop Thomas Cranmer, Bishop Hugh Latimer, and Bishop Nicholas Ridley were locked here for 17 months before being led out to burn at the stake on Broad Street. Cranmer was held the longest, and from the prison he was forced to watch Latimer and Ridley die in the flames below. The prison itself was demolished in 1771, but the original door to the martyrs' cell survives — and you can see it today as you climb the 97 steps of the Saxon tower. You pass through the very doorway the bishops passed through on their way to execution. Along the way, you'll also see a set of 16th–17th century church bells and an original clockwork mechanism before emerging onto the roof with panoramic views of Oxford.