How can you describe the cooler in The Silver Sword?

From the text:

At the back of each block was a leaky and unheated hut known as ‘the cooler’. It had three or four cells to which unruly prisoners were sent to ‘cool off’. To be sent there you only had to be late for roll-call or cheek a guard. It was quite a popular place in summer, as it was so quiet. But in winter you could freeze to death there. In spring, with a bit of luck, you might survive a night or two of frost.