Angkor: Now a listed UNESCO World Heritage site, Angkor's temples are spread over a wide area, though most of the temples are clustered within a 10-kilometre radius of Angkor Wat, and the nearby walled city of Angkor Thom. A few are further out. Varying widely in area from hundreds of acres to less than one, they form a unique ensemble reflecting over six centuries of architectural mastery. The entire site covers several hundred square km and the serious visitor can spend weeks exploring the more than 100 temples. The site lies north of the small but rapidly developing town of Siem Reap.

Built from 879 -1191 AD at the zenith of the Khmer civilization, the temples represent one of the world's most amazing and enduring architectural achievements. From the great citadel of Angkor, the ruling Khmer God-kings controlled a vast territory in the twelfth century, extending south to the Mekong delta in present-day Vietnam, north into Laos, and west over large tracts of what is now Thailand. In its heyday, Angkor had a population of over one million, and was the spiritual center for the Khmers until it was abandoned after being sacked by the Thais in 1431.

For over five hundred years, from the coronation of Jayavarman II in 802 AD, the Khmer Kingdom was the most significant influence upon Southeast Asian development, expanding exponentially at the expense of rival neighbors - Cham, Viet, Burmese and Siamese. The first royal city of Angkor was built by Jayavarman's 10th-century successor, Yasovarman I. It was not until the early twelfth century, and the rule of Suryavarman II that the empire was to reach its peak, and the construction of the magnificent 65-metre tall towers of Angkor Wat was to take place.

After being driven out by the Cham in 1177, the Khmer returned to their city with a new king - Jayavarman VII - a new religion - Mahayana Buddhism - and even higher aspirations for the development of Angkor. The Cham were routed, and Jayavarman VII began construction of the 9-square kilometer Angkor Thom and the 216 faces of the Bayon temple.

By the end, the Khmer empire had constructed over 70 huge temple complexes at Angkor, spread across 200 square km. It is not known why the empire fell into its 200-year decline, however the end came in 1431 when Siamese invaders killed and enslaved much of the population, and stripped the city of its wealth. The Khmer empire was never to recover.

The surviving structures today are but a fraction of the whole picture, which included a huge city whose wooden buildings - houses, markets, shops, palaces, and public buildings - have long since been destroyed by war and time. When French naturalist Henri Mouhot "rediscovered" Angkor, in the mid-nineteenth century, he considered the ruins of the ancient Khmer capital to be "Grander than anything left by Greece or Rome”.

Whilst it is obvious that the Khmers were amongst the greatest architects the world has known, less well recognized was their absolute mastery over water and irrigation. The full extent of the vast system of highly advanced hydrological works, canals and reservoirs that sustained Angkor is only just being understood, since remote sensing and radar images were taken from the space shuttle, Endeavor.

The best sites include:

Angkor Wat: Built to honor the Hindu god Vishnu, is the world's largest religious building and took some 50,000 artisans, workers and slaves, and nearly 40 years, to complete. The temple forms a rectangular enclosure measuring 1,500 meters by 1,300 meters surrounded by a moat 200 meters wide. The main entryway to Angkor Wat is a paved avenue nearly half a kilometer long, ornamented with balustrades and fringed by artificial lakes. Inside the outer walls, the structure rises over three levels to a central core topped by five almost pineapple-shaped towers. Virtually every surface in the maze of chambers and courtyards is richly decorated with low-relief scenes of legends, wars and everyday life, enhanced by carvings of nearly 2,000 apsaras, or celestial dancers. The amazing structure as a whole is best viewed in soft light. Somerset Maugham wrote in 1930: "It needs the glow of sunset or the white brilliance of the moon to give it a loveliness that touches the heart."

The Bayon: At the center of Angkor Thom (literally "Great City"), which forms the heart of the Angkor complex. This inner city is surrounded by a moat, and approached at the four cardinal points via huge stone gates and causeways flanked by statues of gods and giants. The Bayon forms a three-tiered pyramid with 54 towers, each dominated by over 200 huge, 4-metre high, mysterious faces facing out to the north, south, east and west. Each mystically serene countenance, with closed eyelids and faint smile, represents a Bodhisattaya (fully enlightened being) who delays entry into Nirvana to aid the spiritual development of others. The structure is rich in decoration, detailing scenes from battles, religious rituals, and everyday life. On approaching from a distance, it resembles a rather formless initially disappointing jumble of stone, but inside, the visitor discovers a maze of galleries, towers and passageways on three different levels. Under the sightless gaze of the ever-present faces, it is here, particularly if alone, that many tourists experience a feeling of profound spiritual awe.

Ta Promh: If Angkor Wat and the city of Angkor Thom are best known for grandeur and majesty, then the temple and monastery of Ta Promh wins hands down for sheer dramatic effect. Unlike most other monuments, Ta Promh has been left the way it was originally found. The ancient structure is thus still gripped by massive strangler fig and banyan tree roots ("spongs") giving the feeling of discovering the archeological treasure for the first time. Faced with this extraordinary image, it is easy to relive the emotions of the French naturalist Henri Mouhot when he came across it hidden in the jungle in 1860. At its peak, over 70,000 people, including high priests, monks, assistants, dancers and laborers, populated this vast 600-room monastery. The structure measures 145 by 125 meters and contains a maze of courtyards and galleries, many impassable because of the dense overgrowth of creepers and roots.

Prah Kahn: Another temple that has been left to creeping jungle, with huge trees and multi-colored lichen infiltrating the structure's stone corridors and often gloomy interiors. Although it is not as visually arresting as Ta Prohm, this fascinating temple is formed in a cross by a long 200-metre central passageway cut by another wide perpendicular corridor. Both of these have networks of smaller passages, which themselves open to breezeways, courtyards, and rooms of all sizes. Although the central portion is fairly clear, exploring the outer passageways becomes increasingly adventurous with fallen stones, surreal looking tree roots, and tiny apertures leading into almost pitch dark interiors.

Banteay Srei: Approximately 25 kilometers from the main complex, this relatively small 10th century monument in pink sandstone is dedicated to Shiva. Its perfectly proportioned decoration and detail with exquisite sculptures, lintels, and friezes, makes it one of the oldest and most aesthetically beautiful. Almost every surface is a masterpiece of superb detail, each one it seems, more beautiful than the one before.

Phnom Bakheng: Built on the highest hill in the area and offering spectacular views, especially at dawn and sunset, this small but attractive temple makes an ideal start or end to the day's sightseeing, although most tourists congregate here toward dusk.

East Mebon Temple & The Baray Lakes: One of the Khmers' most notable hydrological accomplishments were the West and East Barays, huge, perfectly rectangular artificial lakes covering 14 and 16 square km respectively, and used to irrigate thousands of acres of surrounding farmland. A temple was built in the middle of each lake, and since East Baray was drained, the East Mebon Temple is now easily visited. West Baray (2 km wide & 8 km long) is still filled with water. East Mebon, however, is a fascinating site, best known for the almost life-size stone elephants on the corners of its tiers. Since each one appears to have been hewn from a single block of stone, the task of carving and transporting such huge pieces must have been tremendous. Smaller stone figures flank the stairways leading up to the central elevated platform. From here, the bed of the lake, now fertile paddy, stretches below you in every direction.

The Ruluos Group: Lying approximately 10 km from Siem Reap town, is a cluster of three 9th century temples, namely Prah Ko, Bakong and Lolei. Being the oldest in Angkor, and ostensibly the site of the capital at that time, they are interesting in their own right, particularly Bakong, which is the best preserved of the three. Stairways lined with stone lions lead up the five tiers of the pyramid shaped structure, terminating in a sanctuary on top. Eight small sanctuaries also encircle the base, an architectural concept common to many other Angkor temples.