The Viking Ship Museum is Denmark's national ship museum for vessels of the prehistoric and medieval period, and it exists because of a specific archaeological event. Five Viking ships, deliberately sunk around the year 1070 to block the main fairway into Roskilde Fjord, were excavated at Skuldelev in 1962. They turned out to represent five entirely different types, from bulk cargo carriers to warships. A building was needed, so Erik Christian Sørensen designed one: a hall of concrete and glass overlooking the inlet, opened in 1969 for the sole purpose of displaying them. The ships stand in it as the fragments they are, dark oak and pine held in steel frames, everything the fjord destroyed left as air. Around that core the museum runs research and teaching in maritime history, marine archaeology and experimental archaeology, hosts academic conferences and maintains a research library. It drew 155,745 visitors in 2016.

In 1997 the museum expanded across a drawbridge onto Museumsøen, Museum Island, and set up a boatyard there. This is where the institution stops being a display case. Shipwrights work in the open with axes and augers, splitting oak along the grain the way the originals were split rather than sawing it, and visitors can stand and watch or in some cases join in. The boat collection has grown past forty vessels, gathered from all over Scandinavia, and none of it is static: every summer a handful of boats are launched for extended voyages, because seakeeping, rig behaviour and crew endurance are things a hull will tell you about only when it is loaded, wet and a long way from shore.

The museum has now reconstructed all five Skuldelev ships, each launch a separate piece of research. Roar Ege, from Skuldelev 3, went into the water in 1984. Helge Ask, from the small warship Skuldelev 5, followed in 1991. Kraka Fyr, from Skuldelev 6, launched in 1998, and Ottar, from the ocean-going cargo ship Skuldelev 1, in 2000. Havhingsten fra Glendalough, the reconstruction of the great longship Skuldelev 2, was completed in 2004. Later work has revisited old ground with new arguments: Skjoldungen is a second reading of Skuldelev 6 with a different interpretation of the bow and stern, and Estrid Byrding, launched in 2022, is a second attempt at Skuldelev 3. Where the evidence is ambiguous, the museum builds both answers.

Digging the harbour for that shipyard produced an accident of the best kind. In the late 1990s, excavations for the museum's expansion uncovered the remains of nine more vessels in the fjord mud — the largest such find in northern Europe. Most of the Roskilde ships date from just after the Viking Age, between 1060 and 1350, but one does not. Roskilde 6 was built around 1025 and measures roughly 37 metres, making it the longest Viking ship ever found, longer than anything at Skuldelev. All but Roskilde 8 have been excavated, and the remains went to the National Museum of Denmark, where Roskilde 6 is displayed and the others are in storage. A museum that dug a hole in order to build boats found nine boats in the hole.

The Sea Stallion project cost €1.34 million and ran from August 2000 to September 2004, consuming almost 40,000 hours of labour. Its destination was not arbitrary. Dendrochronology had shown that Skuldelev 2, the original, was built in the Dublin area around 1042, so the reconstruction was sailing back to the yard that made her ancestor. She arrived on 14 August 2007, stayed on exhibit in Dublin until the summer of 2008, then sailed home, reaching Roskilde on 9 August. Every voyage of that kind generates data no excavation can: how a square sail behaves when the wind heads you, how much water comes aboard, how long a crew can keep bailing. The archaeology sits in the hall. The argument about what the archaeology means happens out on the fjord.