About 3 miles

The walk is fully described in the "Think Adventure" website.

When visiting York it is worth first driving to the Park and Ride car park at Rawcliffe Bar (or one of the other Park and Ride places)
The walk starts from Bootham Bar.
The Park and Ride bus stops near there, or there is an alternative bus stop to use at the Lendal Bridge.
Go up the steps at the Bootham Bar, then follow the walls in a Northerly direction, then Soth easterly, until you come to Monk Bar.
Cross over the road and continue at Monk Bar, following the walls until you come to the wall's end (at a tower)
Descend to the street, then head beside the River Foss until you come to the next section of the wall at the Red Tower.
Continue on the wall until you reach York castle.
Cross the road to cross the River Ouse at Skeldersgate Bridge.
Rejoin the Wall and continue to Lendal Bridge.