Is that picture from the prison itself (label "Sigurdur Thordarson in now in Litla Hraun prison in Iceland")? If it is, it looks order(s) of magnitude better than majority of earthlings homes.
But Litla-Hraun is an older building so the cells are not as nice there.
Looking at that picture I'm unsure what makes it "nice" except for the fact that it looks somewhat freshly built.
Cells are cells. What really differentiates prisons is everything around them and what amenities and workshops are offered.
Go look at US prison cells, they're so much worse, there's often no separation between the toilet and the sleeping area.
NYT also wrote a feature about it https://www.nytimes.com/2015/03/29/magazine/the-radical-huma...