The museum opens at 10 and closes at 17. If you arrive late saturday (around 11), plan 30 minutes for the tickets queue.
This museum (130 sek one ticket) is about the Vasa ship, that sank in 1628 (because of construction errors) and was taken out after 333 years, in 1961. The treatment of the wood and the reparations lasted 27 years, and the research of the wood preservation under water continue also today.
You cannot walk inside the ship of course, but you can see all the details of this huge ship from six levels.
(10 sek ~ 1 euro)