1- Mount Athos in Greece

Mount Athos (Άγιο ÎŒρος Ayio Oros, classically Ἅγιον Ὄρος Agion Oros) is a mountain and a peninsula in Macedonia, northern Greece and a UNESCO World Heritage Site.

A fair bit of advance preparation and battling with bureaucracy is necessary to visit Mount Athos, since only 100 Orthodox and 10 non-Orthodox visitors per day are permitted. 

2- Lhasa in Tibet, the Potala Palace

Lhasa, which means "Land of the Gods", is the heart of Tibet. Over 1,300 years old, it sits in a valley right next to the Lhasa River. Tourist resources are plenty, good hotels, tasty restaurants, travel agencies, Chinese department stores and supermarkets, in some parts of the city, you may find no difference to other Chinese cities, but the Tibetan influence is still strong and evident, especially around the old quarters near Barkhor. 

3- Mecca

Mecca or Makkah (in full:(مكة المكرمة Makkah al-Mukarramah), located in western Saudi Arabia, is the holiest city in Islam. As such it is forbidden for Non-Muslims to enter the city. 

A pilgrimage to Mecca, known as the Hajj, is one of the Five Pillars of Sunni Islam and one of the ten Branches of Religion in Shi'a Islam, and thus obligatory for all Muslims with the physical and financial ability to make it. Over three million Muslims visit the city during the month of Dhu'l-Hijjah yearly. Visits outside this month are known as minor pilgrimages or Umrah, and while not compulsory are strongly encouraged.

4- Vatican

Perhaps the Vatican needs no introduction. The center of Catholicism, and encompassing the Vatican City state, as well as the surrounding Roman neighborhoods of the Vaticano, Prati, and Monte Mario, this small slice of the city is packed with more history and artwork than most cities in the world.

Do you know any other places? Please feel free to advice and post it here :)

Click on the photo to see more photos of these Holly Places.

Personal , I'd love to visit the Potala Palace!