Since 1954 the two oldest parts of the castle have been Grade I listed buildings: the 11th-century motte with its 13th-century well-chamber,[64] the circa 11th-century St George's tower (listed as Norman, but now generally believed to be Saxon), the relocated crypt chapel, and the 18th-century D-wing and Debtors' Tower.[58] The site is protected as a Scheduled Monument.[65] As at 2018, guided tours of the surviving medieval and 18th century portions are available to visitors via a commercial operator, Heritage Projects (Oxford Castle) Ltd, with opening hours and pricing available via their website.[66]