This museum is actually an intact royal warship, the Vasa, which capsized in Stockholm harbor on its maiden voyage in 1628 and was salvaged in the 1950s, with other exhibits about life on the ship and the salvage and restoration processes. The ship was preserved for more than 300 years on the seabed, close to the site of the museum, by the brackish water of the Baltic Sea and Lake Mälaren. It was one of my favorite attractions in Stockholm.
I thought the architecture of the museum was quite interesting, built to accommodate this gigantic vessel. The masts in the picture aren't those of the Vasa, but two of the original masts are still attached to the ship.