A small island of half-timbered houses around the Marktkirche and the Altes Rathaus, plus a couple of streets of brick alleys behind. Almost all of it is post-war reconstruction — the medieval Old Town was flattened in 1943 and what stands now is a careful 1950s "new old town" assembled from surviving fragments.
The Holzmarkt, the Kramerstraße and the Leibnizhaus (a baroque facade reattached to a new building) are the picture-postcard corners. An hour's wander does it.