Lufthansa: Visit the oldest and biggest open-air museum of the world: The Skansen on the island Djurgården. This great museum also houses Stockholm's zoo as well as really nice restaurants and cafes. Ha så kul!
Lufthansa: "Under the Bridges" is a sightseeing tour of Stockholm by boat. It takes you around the new and old neighborhoods, giving a good overview of the city which should really be seen from the water once.