This museum is actually a royal warship that capsized in Stockholm harbor in 1628 and was salvaged in the 1950s, with other exhibits about life on the ship and the salvage and restoration processes. It was one of my favorite attractions in Stockholm. It was closed that evening, but we did return several days later to tour the museum, so pictures will be coming.
These aren't the actual masts of the ship, but two of the original masts are still attached to the vessel inside.