The Tholsel is Kilkenny's old city hall, standing on High Street in the middle of the Medieval Mile. Its arcaded ground floor and octagonal clock tower make it one of the most recognisable civic buildings in the city, even though many visitors pass it on the way between the castle and St Canice's without knowing what it is.
It is not a long visit, and you may only see the exterior, but it anchors the street beautifully. Pause under the arches, look up at the tower, and use it as a marker for Kilkenny's trading past rather than just another pretty stop on the walk.