I generally do not have terribly high expectations for hostels. Just need a bed and a place to eat. But Langholmen made me realize that I actually have a few other fairly basic preferences. Or rather, needs.
Like ventilation (stale smell in the hallways). And somewhere to chat with others. And light. And breakfasts that come in under $10. I noted on here that they are apparently a large spread but if you stay for more than three days you're easily meeting the amount of a full nights stay just in breakfast! (currently about $13 American).
I appreciate that it is a unique and novel idea but I pulled the trigger on leaving early when a cockroach ran past the outlet I had my phone plugged into.
In their defense of one complaint, I also have a unique need in that i have some back problems. Where some folks may have noted that the beds were comfortable, the thin pads unfortunately exacerbated my condition. Can't really blame the hostel for that though.
My biggest issue was that, given the time of year I stayed and the poor location of Langholmen outside the city, once 10 o'clock rolled around and my roommates went to sleep there was complete and utter silence. no birds, no heating system sounds, no water pipes. No signs of life. After laying awake for hours listening to my ears ring from the excessive quiet I gave in at about 4 AM and booked a hotel for my last night. If you are a city folk and find comfort in having people around this is NOT the place for you!

I will close out with the good things so as not to deter if you are ok with the above: The registration area is very welcoming. The museum is interesting. Bathrooms are very clean and showers are comfortable. Kitchen is functional and even though it is pretty far out, it's walkable to transportation.

In all fairness I will say this: Go during summer with your buddies, you will have a much better experience.

I have been 2 nigths in the hostel. Was pretty difficult from the metro station to find it, and when i was there i feel strange. I was staying where years ago, people couldn´t go out... is the concept what i feeel dissapointed with, because it is quite sarcastic to pay for some cool place in where you can read and see how the prisioners were living in. I did it and afterwards it leaves to be cool to become in sarcastic. Besides the concept, my room was a 4-beds one with a share toilet.
like in other hostels, but i miss a common area to enjoy and meet people: they have a rest-area but i don´t feel that was a place in where stay talking and having a good time with others as the rooms are just beside it and you can disturb the other guests.
great area, I´ve seen a fox in the park!!! that is amazing! Enjoy your visit and enjoy the wonderful city of Stockholm!!

We stayed in this unique hotel for a few days.
It's a bit out of the centre but the metro runs often.
The island that the hotel is on is worth a quick walk around after breakfast, which is the typical scandanavian smorgasboard, was what you would expect.

Now the bad part, the housekeeping was not up to standard. The glasses were not cleaned on our stay, neither were the towls they were not replaced just folded and put back on the warmer. Not enough paper was left in the toilet, but the room was spotless when we first entered it, it was just the day to day upkeep that had problems.

This is a hostel that used to be a prison. Your room is a prisoner's cell, and is as tiny as can be expected. The bunk bed was comfortable, the bathroom barely big enough to turn around in , and they had a TV. It was a fun and enjoyable stay, considering that you are not in a hotel - but a hostel-like accommodation. If you like creepy situations and haunted houses, this is the hostel for you :) I did not dine there, so cannot comment on food/restaurant.