The day I visited I had the best possible tour guide. She was funny, eager to share her knowledge and showed lors of passion and dedication for this beautiful building. It's a great enlightening learning experience.
Nice building, but that all I can say, I wasn't allowed inside. It is on the main street from the city to the Gamla Stan (old City) and the Royal Palace therefore you can not miss it or ignore it. It is a busy place for the same reason. Definitely a point of interest.
Great place to take pictures especially at night when it and the Royal palace just down the street are all lit up. Tours are free but check early as they are not done on Mondays and are cancelled frequently when parliament is in session.