The Kaaba (Arabic: الكعبة) House of Allah (Creator and Honour of Everything) is very first building built on earth, Designed by Hazrat Ibrahim (Ala Nabiiena wa Alahis Salat o Wassalm) Located in Mecca, Saudi Arabia, and is the most sacred site in Islam.
The building predates Islam, The building has a Masjid built around it, the Masjid al-Haram. All Muslims around the world face the Kaaba during prayers, no matter where they are.
One of the Five Pillars of Islam requires every capable Muslim to perform the Hajj pilgrimage at least once in their lifetime if they can. Multiple parts of the Hajj require pilgrims to walk several times around the Kaaba in a counter-clockwise direction (as viewed from above). This circumambulation, the Tawaf, is also performed by pilgrims during the Umrah (lesser pilgrimage). However, the most dramatic times are during the Hajj, when two million pilgrims simultaneously gather to circle the building on the same day.