Not familiar with this particular place, but Confederate prisoners in New Orleans were generally held in several of the various cotton presses throughout the town. (Officers were held at the Custom House, which is still in existence on Canal Street.) A cotton press is a warehouse where cotton was brought to be pressed and stored before shipment from the port. The cotton had to be "pressed" because your typical plantation gin did not have a tremendous amount of power, and the cotton bales that they delivered to New Orleans were of all different dimensions and densities. At the press, the bales would be re-pressed and compacted much tighter than they were when they arrived, which meant a lot more bales could be stored in the hold of the ships. Once the bales were compacted, they were stored there at the warehouse until shipment. Since there wasn't much cotton being shipped from New Orleans during the war, there were a lot of these warehouses sitting empty. They were used to hold POWs during the war.