Hall of the two Sisters. This hall got its name from the two very beautiful white marble slabs laid as part of the pavement. There is a fountain in the middle of this hall, and the roof - a dome honeycombed with around 5000 tiny cells which are all different, it is a magnificent example of the so-called "stalactite vaulting" of the Moors. The most impressive part of the hall is the beautiful and perfect dome of mocarabes. Its lighting was carefully considered and it receives light from small windows.
It has been suggested that the ceiling may have had an acoustic function because the hall was used for music recitals. This style of ceiling effect is called Muqarnas. Muqarnas is known in Iberian architecture as Mocárabe, it is a form of ornamented vaulting in Islamic architecture. It is sometimes called "honeycomb vaulting" or "stalactite vaulting", the purpose of muqarnas is to create a smooth, decorative zone of transition in an otherwise bare, structural space. This structure gives the ability to distinguish between the main parts of a building, and serve as a transition from the walls of a room into a domed ceiling.
Muqarnas is significant in Islamic architecture because its elaborate form is a symbolic representation of universal creation by God. Muqarnas architecture is featured in domes, half-dome entrances, rectangular halls or enlarged niches.