Today, it is merely a tourist attraction but a thousand years ago, at the peak of the Viking kingdom, sighting such a boat usually meant big trouble for the locals.

As an aside, this ship was built from scratch using only manual tools, equipment and materials, corresponding to the level of technology at the time such long boats were built. More info on the website of the Viking Ship Museum in Roskilde, Denmark:
https://www.vikingeskibsmuseet.dk/en/professions/boatyard/