If you like photos, Fotografiska is the place to go to when in Stockholm. Fotografiska can be found on Stadsgårdshamnen 22 in Södermalm, in and old tollhouse close to the water. Go to Slussen and follow the street near the water and you cannot miss it. It opened in 2010 and has an exhibition space of 2'500 squaremeters. There have been exhibitions of some popular photographers such as Annie Leibovitz, Nick Brandt and also some guy called Bryan Adams. You can find their current exhibitions on their website. The entrance fee is SEK 155 for a day ticket, free for kids under 12. The opening hours might surprise you: Sunday to Wednesday 9am to 11pm and Thursday to Saturday 9am to 1am. Yes, 1 am. So as the sun goes down quite late in summer in Stockholm, you can stay outside for the sunset and visit the museum when it's dark. Or almost.
Other than the fantastic exhibitions, you have a beautiful view on Gamla stan and in summer you can sit outside for some drinks and snacks. Sometimes there are also concerts. And of course some food inside, for example the award-winning Fotografiska Restaurant with a stunning view. Unfortunately it's closed in summer, but check it out when being there on any other time of the year. And there is also a shop where you can find hundreds of books of famous photographers.
Plan some hours for your visit and enjoy it!