Goslar packs a thousand years of imperial and mining history into a walkable old town the size of a few city blocks. The Kaiserpfalz and the Rammelsberg mine together form a single UNESCO World Heritage site, and either deserves half a day on its own. A long weekend gives you time for the half-timbered backstreets, the small museums tucked behind the market square, and a walk out to the Oberharz mining ponds above town.