You can see what a cat pen looks like here.
The cats are kept separately, although cats from the same home can share a pen. The pens have solid sides to prevent spitting or scratching from the cat next door. The fronts are made of mesh so that cats have plenty of air and can see out. Some of the pens have a small outdoor run. We heat the cattery when it is cold and let fresh air in with mesh doors when it is warm. There are shelves at different heights that the cats enjoy to sit and sleep on. We provide bedding, litter trays, scratching posts and bowls.
Looking into a cat pen. 
Some pens have outside runs. 
Cats love the shelves to rest on.