Mecca
The Kaaba, the small cubical building which Muslims pray towards is believed to have been built by Ibrahim and has been a religious center ever since. Muslims believed that God commanded Ibrahim to send his second wife Hajar and her son Ismail there. They found the Zamzam Well which led to people settling nearby, and thus Makkah was born. When Ismail was big enough, he helped his father to build the Kaaba. The Kaaba is the place towards which Muslims turn in prayer. This is known as the Qibla.