The dungeons were used for locking up captive prisoners who were lowered down on ropes into the main hole. In general the dungeons of the Alhambra had a bottle-neck shape and most contained small spaces dug out of the terrain and separated by bricks, where the captives could lie down in makeshift independent sleeping spaces. The central space was open to the air and normally had a drain with marks on the ground. These underground chambers were also used as silos, as stores for grain, spices and salt. A total of twelve dungeons have been found in the Alhambra. Several of these are inside the Alcazaba, which has two under the Homage Tower and the Bell Tower (Torre del Homenaje and Torre de la Vela). A third can be found at the base of the Broken Tower (Torre Quebrada), which according to the Official Alhambra Guide Book is perhaps one of the most interesting surviving dungeons, due to its structure and the visible remnants, such that in the 1930s a spiral staircase was installed to make it easier to enter.