Which is the most sacred place to Muslims?

The Kaaba also referred as al-Kaʿbah al-Musharrafah (Arabic: the Holy Kaaba), is a building at the center of Islam's most important mosque, that is Al-Masjid Al-Ḥarām (The Sacred Mosque), in the Hejazi city of Mecca, Saudi Arabia. It is the most sacred site in Islam. It is considered by Muslims to be the Bayṫ Allāh ("House of God"), and has a similar role to the Tabernacle and Holy of Holies in Judaism. Wherever they are in the world, Muslims are expected to face the Kaaba when performing Ṣalâṫ (Islamic prayer). Being the qiblah (direction of prayer), Muslims would face it when praying.

The Kaaba is a prismal stone structure made of granite. Inside the Kaaba, the floor is made of marble and limestone. The interior walls are clad with tiled, white marble halfway to the roof, with darker trimmings along the floor. The floor of the interior stands about 2.2 m (7.2 ft) above the ground area where tawaf is performed. Tawaf is one of the Islamic rituals of pilgrimage.