Many know this town—Denmark's first capital—only for the Roskilde Festival, the huge outdoor rock-music festival held there annually over the last weekend of June. Check the dates—you'll either want to buy tickets for the show or avoid the town altogether. The ornate cathedral, which dominates the center of town and is the final resting place for Denmark's long line of royalty, is worth a visit. Don't miss the 16th-century clock inside, with St. George and a dragon.
Additional nearby sights of interest are
Lejre (an excavation site in the center of Sjaelland Island with a 260-ft-/80-m-long Viking burial site shaped like a ship); and
Trelleborg (a fortified construction in Sjaelland that probably served as a training camp for the king's men before expeditions to the British Isles).
Roskilde is 20 mi/32 km west of Copenhagen.