The hostel and its rooms were clean and, although simple, felt fresh and very much as expected from hostel standards. Our party of three people had two rooms booked but we could have easily fit in one as the first room had a king size + a single bed, and the other room had a king size + a two story bunk bed. I think, however, that it wasn't possible to book one room for three adults on the web page.
The place was right outside the Karlsborg fortress and would be perfect for tourists visiting the place.
The beds were comfortable and spacious. You have to bring your own sheets unless you're paying for the hotel experience which also includes breakfast.
The one complaint I have is that it was very cold in the rooms, we slept with multiple layers of clothes. This may be due to the fact that we visited on the last weekend of October, which also happened to be the first really cold weekend of the season (around 0-3 degrees Celsius during both day and night). Perhaps the radiators need some time to adapt to the outside cold. However this is a non-issue for summer visits.
The receptionist was really nice and gave us our keys in cute little envelopes with our names neatly handwritten on them!
All in all it was a really nice stay for such a low price and I will definitely consider booking this place again if I go back to Karlsborg.