For lost-world ambience, the Preah Khan Temple Enclosure can't be beaten. Covering almost 5 sq km, this temple complex (not to be confused with the temple of the same name at Angkor) is the largest temple enclosure constructed during the Angkorian period – quite a feat when you consider the competition.
Preah Khan’s history is shrouded in mystery, but it was long an important religious site, and some structures here date back to the 9th century. Both Suryavarman II, builder of Angkor Wat, and Jayavarman VII lived here at various times during their lives, suggesting Preah Khan was something of a second city in the Angkorian Empire.
Originally dedicated to Hindu deities, Preah Khan was re-consecrated to Mahayana Buddhist worship during a monumental reconstruction in the late 12th and early 13th centuries.
Wrapped by vines and trees, and thanks to its back-of-beyond location, the site is astonishingly peaceful and you'll very likely be the only visitor. One entry fee gains you admission to all of the temples in the enclosure.