Roskilde was Denmark's capital for most of the Middle Ages, and two landmarks from that era still define the town. The Viking Ship Museum on the harbour displays five original Viking ships recovered from the fjord, where they had been deliberately sunk a thousand years ago to block the waterway. You can watch boat-builders working with period tools in the workshop, and in summer you can sail on a reconstructed Viking longship on Roskilde Fjord.
Roskilde Cathedral, a UNESCO World Heritage Site, has been the burial church of Danish monarchs since the fifteenth century — over forty kings and queens rest in its chapels, each in a more elaborate sarcophagus than the last. The cathedral's twin spires dominate the skyline and are visible from the train well before you arrive. Beside it sits Roskilde Palace, now a contemporary art museum.
The town itself is compact and pleasant, with a good café culture around Stændertorvet, the central square. The Roskilde Museum fills in the town's history between the Viking Age and the present. Every June, the Roskilde Festival takes over a field south of town — the largest music festival in northern Europe and one of the oldest in the world. Most visitors come as a day trip from Copenhagen, just twenty-five minutes away by train, but Roskilde rewards a full day.