There are three main holy places in Islam.
1. Makkah, Saudi Arabia
2. Madinah, Saudi Arabia
3. Al'Quds (Jerusalem), Palestine
All three are holy, though Makkah maybe considered the holiest due to it being the first place where a house of God was built on earth, as mentioned in the Qur'an. Also the Prophet, peace be upon him, said prayer in Makkah (not only the Masjid) is worth 100 000 times more than praying elsewhere. Whereas, Madinah the prayer is 1000 more in the Prophet's Masjid; and the Masjid in Al'Quds, aka Masjid Al'Aqsa, is only 500.
Mecca
If by the Sacred Mosque you mean the Great Mosque in Mecca, yes it is.
The holiest city for the Muslims is Makka (Mecca) situated in Saudi Arabia.
The holiest city for the Muslims is Makkah(Mecca),S.Arabia
Mecca (or Makkah) is forbidden for non Muslims to visit or stay because it is the Muslims most sacred and most holiest city. It is the same way Vatican is forbidden for Muslims to stay in.
Maaka is the best place on the earth for Muslims.
The third holiest Islamic city
The major place in Suadi Arabia is Mecca. Mecca is regarded as the Holiest city in the Religion of Islam. The Kaaba is located in Mecca and in ramadan muslims go there for Hajj.
Al-Quds (or Jerusalem) in the Palestinian Territory
Muslims pray facing the holiest of cities in Islam--Mecca, Saudi Arabia.
No, non-Muslims are not allowed to visit Mecca, as it is considered the holiest city in Islam and only Muslims are permitted to enter.
Unlike Judaism (Jerusalem) or Islam (Mecca), there is no "holiest place of worship for Christians."