Walking the full circuit of York's medieval walls is the single best free thing you can do in the city. The walls survive almost entirely intact for 2.5 miles and the walkway on top of them gives views that no street-level touring can match: over the Minster and the old city to the north, the city gardens and the railway to the south. The medieval bar gates. Micklegate Bar, Bootham Bar, Monk Bar, Walmgate Bar, each have their own character.
The full circuit takes about 2 hours at a comfortable pace. The stretch from Bootham Bar to Monk Bar, closest to the Minster, is the most atmospheric. Come in morning light for the best photography.