Wikipedia has an extensive article about Angkor Wat. The following is from the History section that discusses the transition from Hindu to Buddhist Temple. From (
visit link)
"The initial design and construction of the temple took place in the first half of the 12th century, during the reign of Suryavarman II (ruled 1113 – c. 1150). Dedicated to Vishnu, it was built as the king's state temple and capital city. As neither the foundation stela nor any contemporary inscriptions referring to the temple have been found, its original name is unknown, but it may have been known as "Varah Vishnu-lok" (literally "Holy Vishnu Location", Old Khmer Cl. Sanskrit") after the presiding deity. Work seems to have ended shortly after the king's death, leaving some of the bas-relief decoration unfinished. In 1177, approximately 27 years after the death of Suryavarman II, Angkor was sacked by the Chams, the traditional enemies of the Khmer. Thereafter the empire was restored by a new king, Jayavarman VII, who established a new capital and state temple (Angkor Thom and the Bayon respectively) a few kilometres to the north.
In the late 13th century, Angkor Wat gradually moved from Hindu to Theravada Buddhist use, which continues to the present day. Angkor Wat is unusual among the Angkor temples in that although it was somewhat neglected after the 16th century it was never completely abandoned, its preservation being due in part to the fact that its moat also provided some protection from encroachment by the jungle.
One of the first Western visitors to the temple was António da Madalena, a Portuguese monk who visited in 1586 and said that it "is of such extraordinary construction that it is not possible to describe it with a pen, particularly since it is like no other building in the world. It has towers and decoration and all the refinements which the human genius can conceive of." In the mid-19th century the temple was visited by the French naturalist and explorer, Henri Mouhot, who popularised the site in the West through the publication of travel notes, in which he wrote:
"One of these temples—a rival to that of Solomon, and erected by some ancient Michelangelo—might take an honourable place beside our most beautiful buildings. It is grander than anything left to us by Greece or Rome, and presents a sad contrast to the state of barbarism in which the nation is now plunged."
Mouhot, like other early Western visitors, found it difficult to believe that the Khmers could have built the temple, and mistakenly dated it to around the same era as Rome. The true history of Angkor Wat was pieced together only from stylistic and epigraphic evidence accumulated during the subsequent clearing and restoration work carried out across the whole Angkor site. There were no ordinary dwellings or houses or other signs of settlement including cooking utensils, weapons, or items of clothing usually found at ancient sites. Instead there is the evidence of the monuments themselves."