Bury St Edmunds Abbey is the reason the town exists. The ruins are fragmentary now, but their scale still comes through in the layout: flint walls, broken arches, the remains of the great west front, and gardens where one of medieval England's richest Benedictine houses once received pilgrims to St Edmund's shrine.
The abbey gardens make the site unusually easy to enjoy. You can wander without a ticket, sit on the lawns, and let the ruins emerge between flowerbeds, mature trees, and the cathedral precinct. It is atmospheric rather than complete, which suits Bury well: the missing masonry leaves enough space for imagination.