I hate to give this gem away :) (because I love this place) but I will feel sorry for anybody who happens to be in stockholm while its raining. Therefore, I am giving this gem away to any and all tourists that plan to visit stockholm.
In addtion to the obvious museums like Vasa museum, Modern Museum etc. there is an unbelievable IMAX theatre where you can watch the most amazing documentaries on various topics. The place is called COSMONOVA.
Check and out research this site and you will thank me afterwards. Trust my word!