Linda B.
Google
This kind of hidden museum tells the early story of Stockholm, and you can se the remains of the first city wall, which was actually not discovered until the end of the 20th century.
In the museum, you can see a lot of exciting displays, and there are things for kids as well.
Best of all, the museum is free, and you can store your luggage for free as well.
In order to find the entrance, you actually have to walk around the Parliament and then enter from the basement.
Visited with my brother and my teenage daughter. They too found it interesting.