The Orthodox Monastery of St Catherine is set in a rugged mountain landscape in Sinai, Egypt, at the foot of Mount Horeb where Moses received the Tablets of the Law according to the Old Testament. The mountain is known and revered by Muslims as Jebel Musa. The entire area is sacred to three world religions: Christianity, Islam, and Judaism. The Monastery was founded in the 6th century and is one of the oldest Christian monasteries still in use for its initial function. Its walls and buildings are of great significance to studies of Byzantine architecture, and the Monastery houses collections of early Christian manuscripts and icons. 

The monastery was built by order of the Emperor Justinian between 527 and 565 to house the remains of St. Catherine of Alexandria. St. Catherine, whose body was reportedly carried away by angels, was discovered five hundred years later at the top Mount St Catherine (2642m). Her relics are buried in a marble reliquary in the basilica.

St Catherine’s contains works of art, including Arab mosaics, Greek and Russian icons, Western oil paintings, paintings on wax, fine sacerdotal ornaments, marbles, enamels, chalices, reliquaries, including one donated by Czar Alexander II in the 19th century, and another by Empress Catherine of Russia in the 17th century. 

It also houses the second largest collection of illuminated manuscripts (The Vatican has the largest). The collection consists of some 3,500 volumes in Greek, Coptic, Arabic, Armenian, Hebrew, Slavic, Syriac, Georgian and other languages. Around the year 1850, the fourth century Codex Sinaiticus, which is now in the British Museum in London, was discovered here.
Inside the Monastery wall there is a small Fatimid mosque from the 11th C.

There is also a small chapel (the Chapel of St. Triphone, also known as the Skull House) which houses the skulls of deceased monks.
Though established and patronized most of its history by the Russian Orthodox Church, it is now under the auspices of the Greek Orthodox Church. Most of its monks are also of Greek origin.

The area of St. Catherine Protectorate was named a UNESCO World Heritage Site in 2002 according to the following criteria:

Justification for Inscription

Criterion 1: The architecture of St Catherine's Monastery, the artistic treasures that it houses, and its domestic integration into a rugged landscape combine to make it an outstanding example of human creative genius. 

Criterion 2: St Catherine's Monastery is one of the very early outstanding examples in Eastern tradition of a Christian monastic settlement located in a remote area. It demonstrates an intimate relationship between natural grandeur and spiritual commitment.

Criterion 3: Ascetic monasticism in remote areas prevailed in the early Christian church and resulted in the establishment of monastic communities in remote places. St Catherine's Monastery is one of the earliest of these and the oldest to have survived intact, being used for its initial function without interruption since the 6th century.

Criterion 4: The St Catherine’s area, centred on the holy mountain of Mount Sinaï (Jebel Musa, Mount Horeb), like the Old City of Jerusalem, is sacred to three world religions: Christianity, Islam, and Judaism.

http://whc.unesco.org/en/list/954

photo sources : http://interoz.com/egypt/Sc07.htm ; www.markhorrell.com/travel/egypt/sinai