I spent 2 weeks in Stockholm once on business but got the weekend in the middle free.
The thing I did that has left a lasting impression on me was to visit the Vasa museum.
This is the remains of an almost totally preserved "Tudor" ship that sunk in the harbour in Stockholm on its maiden voyage and was brought back to the surface about 20 years ago, and they floated it into a dry dock and built a museum round it.
They have since found loads of belongings from the ship at the bottom of the sea and they are in the museum.
This is one of the most amazing museums I have ever visited.
More here
http://www.visitstock...s/the-vasa-museum/142