In Muslim religious practice, worshippers must all turn to face one single direction during daily prayers. This qiblah is the direction of the Ka'aba in Mecca, in modern-day Saudi Arabia. When possible, mosques are constructed in such a way that one side of the building faces the qiblah, to make it easier to organize worshippers into rows for prayer. The direction of the qiblah is also often marked in the front of the mosque with an ornamental indentation in the wall, known as a mihrab.
It should be noted that Muslims do not worship the Ka'aba. The Ka'aba is a capital and focal point of the entire Muslim world.