The Roskilde Festival, held annually in late June and early July, is the largest music festival in northern Europe and one of the oldest outdoor rock festivals in the world. The festival site — a large field south of the town centre — hosts around 130,000 people over four days, with eight stages covering rock, hip-hop, electronic, and world music.
Outside festival week the site is quiet, but a visit to understand its scale is oddly worthwhile — the infrastructure is enormous and permanent, and the walk from the station to the main stage gives you a sense of the event's ambition. For the festival itself, book far in advance; tickets sell out months ahead of the lineup announcement, which gives you some sense of how committed the audience is.