York, located in Yorkshire, England, in the banks of the River Ouse River, Leeds ENE. The city has a rich heritage and has provided the backdrop to major political events throughout much of its two millennia of existence.York Minster, the largest Gothic cathedral in northern Europe, stands at the city's centre. Clifford's Tower, part of York Castle York Castle, a complex of buildings ranging from the medieval Clifford's Tower to the 20th century entrance to the York Castle Museum (formerly a prison) has had a chequered history. York's centre is enclosed by the city's medieval walls, which are a popular walk. These defences are the most complete in England. They have the only walls set on high ramparts and they retain all their principal gateways. They incorporate part of the walls of the Roman fortress and some Norman and medieval work, as well as 19th- and 20th-century renovations.