Few of the things to see, during the summer in Stockholm are:
-The art exhibitions.
My favorite one is the: Helmut Newton exhibition at Fotografiska in Stockholm.
He was known especially for his fashion and nude/provocative pictures, most of them black-and-white.
Most iconic picture is called Le Smoking that he shot of Marlene Dietrich dressed in Yves Saint Laurent. It expresses a chic, timeless and androgynous look.