Langholmen hostel
The Langholmen concept is quite original, you sleep in the dorms of an old prison. The experience is unique, but if you just want an affordable bed to sleep there are cheaper options. This is not a party hostel either.
The dorms are located in the prison museum where you have an exhibition. The heavy doors open to a reasonably sized bedroom with comfortable beds and decent lockers, but you have to pay extra for everything else: linen, towels, internet, breakfast…
You can have breakfast for 80kr, its not pricey for what you get considering Stockholm prices, since you have a buffet with all sort of good food (just missing some fruit!).
The location of the hostel is also quite pleasant, one of Stockholm lovely islands, with several nature paths and a beach! Also not too far from the metro and in a walkable distance to the city center (20min) through a path by the water.
The staff is really friendly and helpful which is a plus.