The epic Nordiska Museet is Sweden’s largest cultural-history museum and one of its largest indoor spaces. The building itself (from 1907) is an eclectic, Renaissance-style castle designed by Isak Gustav Clason, who also drew up Östermalms Saluhall; you'll notice a resemblance. Inside is a sprawling collection of all things Swedish, from sacred Sámi objects to clothing and table settings. The museum boasts the world’s largest collection of paintings by August Strindberg, as well as a number of his personal possessions.
In all, there are over 1.5 million items in the museum's collection, dating from 1520 to the present day. It's unusual as far as museums go for being curated around various ideas of what it means to live in the Nordics in the broadest sense, going as far back as 500 years and speculating into the future. Topping it off are the often dynamic temporary exhibitions. The insightful audio guide (free with admission) offers several hours of English commentary.
The new top-floor exhibition, Nordbor, opened in 2024 and covers 500 years of Swedish cultural history. A giant wooden statue of Gustav Vasa by Carl Milles overlooks the main hall and there's a wonderful exhibit that showcases the impact of climate change on the people who live in the Arctic. There is also an installation dedicated to festivals and celebrations from the region.
Ask at the ticket desk about guided tours which, if you're pressed for time, can be whittled down to as little as one hour. The museum is free for children under 18.