The center prayer space inside is known as a musalla (literally, "place for prayer"). It is purposefully left naked. Worshippers sit, kneel, and bow straight on the floor, hence no furniture is required. There may be a few seats or benches available to help elderly or handicapped worshipers who have difficulties moving around. A musalla can also be called a dar-us-salasah ("a place of prostration"). In addition to the central prayer space, some mosques have side-chapels that are used for prayer. These are called jamaat-us-salaah ("places for congregation"). There are three types of spaces in a mosque that are used for prayer: the kaaba, the hajj, and the mashq. The kaaba is the name given to the physical structure that constitutes Islam's holiest shrine; it is located in the city of Mecca, Saudi Arabia. The location of the actual stone from which Muhammad is believed to have taken prayers is unknown. What is known is that the original rock was moved to a new site when the old one was destroyed during the Hajj pilgrimage. The new site is called al-Haram ash-shafa'i ("the forbidden enclosure"). The hajj is the annual pilgrimage to Mecca that must be performed by any Muslim who is physically and financially able to make the trip.