They can be. If you're curious, check out "worlds toughest prisons" on Netflix, an episode that shows a Norwegian rehabilitation-focused prison. You can see how the place is both secure and warm.
I've seen pictures of Norwegian prisons. They certainly look comfortable, but I wouldn't describe them as "open, warm, and inviting". They look halfway between a no-frills dorm and the psychiatric ward I stayed in for a while as a teenager. Certainly far more humane than American prisons, but still clearly _institutional_.
