There are several options to do tours in Mecca. Here are few places to see. For all Muslims the holy mosque (The Masjid Ul Haram) where the Kaaba the house of Allah is built is the most important to see.
Sacred Mosque (al-Masjid al-Haram). The holiest site in Mecca and Islam. This mosque is built around Kaaba. At the center of the sacred mosque is this building, said to have been built by Prophet Abraham himself and his son, Prophet Ishmael. Covered in black cloth, it is circled seven times by Muslim pilgrims.