Leeds' most impressive medieval structure is beautiful Kirkstall Abbey, founded in 1152 by Cistercian monks from Fountains Abbey in North Yorkshire. These days the city makes good use of it as an atmospheric backdrop for pop-up events and a monthly weekend food market (April to November; check online for dates). It's 3 miles northwest of the centre; take bus 33, 33A or 757.
Across the road is the Abbey House Museum.