A picture of the small cold pool in the men's frigidarium. Note the remnants of plaster and frescoes on the walls as well as the niches for statues.
The Stabian Baths were the oldest and largest baths in Pompeii and were constructed in the second century B.C. They included a (un)dressing room (apodyterium), a medium temperature room (tepidarium), a hot room (caldarium), and a cold room (frigidarium). One usually proceeded through the bath in that order. Besides these usual rooms, they included a men's and a women's sections (thus baths), a large open exercise area (palestra), and a swimming pool.
The earthquake of A.D. 62 severely damaged these baths and some areas were not in use at the time of the eruption of Vesuvius.