Deep in the forests of Cambodia’s Siem Reap province, the elegant spires of an ancient stone city soar skyward above the sprawling complex of Angkor Archaeological Park.

The Khmer Empire’s various capitals thrived here from the 9th to 15th centuries, while their rulers presided over an empire that stretched from Myanmar (Burma) to Vietnam. Including forested areas and newly discovered “suburbs” Angkor covers more than 400 square kilometers.

Though just one of hundreds of surviving temples and structures, the massive Angkor Wat is the most famed of all Cambodia’s temples—it appears on the nation’s flag—and it is revered for good reason. The 12th century “temple-mountain” was built as a spiritual home for the Hindu god Vishnu. The temple is an architectural triumph laden with artistic treasures like the bas-relief galleries that line many walls and tell enduring tales of Cambodian history and legend.

In other parts of Angkor such art depicts scenes of daily life—offering scholars a precious window into the past.

One tale Angkor’s artists and scribes did not tell, however, is why the city’s rulers abandoned the site and resettled near modern Phnom Penh. Theories include defeats in battle and shifting religious observances, (because the Khmer’s Hinduism was gradually replaced by Theravada Buddhism during the 13th and 14th centuries), but the mystery has puzzled scientists for centuries.

Angkor is as much about water as it is about stone—the site boasts an enormous system of artificial canals, dikes, and reservoirs, the largest of which (West Baray) is 5 miles (8 kilometers) long and 1.5 miles (2.4 kilometers) wide. These incredible feats of engineering form an integral part of an overall site design that remains faithful to religious symbolism. Moats, for example, simulate the oceans surrounding Mount Meru, the home of Hindu gods.

But these massive works also served a practical purpose by skillfully harnessing river and rainwater to quench the thirst of some 750,000 residents in the world’s largest preindustrial city. That water also irrigated wealth-producing crops like rice, which served the Khmer as currency.

Some scholars speculate that the downfall of this elaborate water system led to the end of Angkor. A series of weak monsoons and/or the collapse of the water works due to environmental issues, like deforestation, which drove destructive floods and choked the system with sediment, might have tipped the movement of power toward Phnom Penh.

Even after its glory days had passed, Angkor remained popular with Buddhist pilgrims who journeyed from across Southeast Asia and beyond. Today the site also draws secular travelers—almost a million a year.

When Angkor was named a World Heritage site in 1992 it was also added to the List of World Heritage in Danger; the incomparable site was threatened by pillaging, plagued by illegal excavations, and even dotted with land mines. In 1993 UNESCO launched a major campaign to restore and safeguard Angkor. Thanks to a textbook case of international cooperation Angkor rebounded so dramatically that it was removed from the List of World Heritage in Danger in 2004. [Related: 25 World Heritage Sites in Danger]

UNESCO continues to be a part of Angkor’s future, working with the Cambodian authorities to ensure that tourism access and development do not compromise this great cultural treasure.

View Images Strangler fig trees and creeping lichens devour ruins at Ta Prohm at Angkor, once home to hundreds of monks. Photograph by Paul Chelsey, National Geographic

How to Get There

The nearby town of Siem Reap can be reached via good roads from Phnom Penh and buses and taxis make the trip regularly. Those preferring to travel by boat can also make the trip from Phnom Penh in some five or six hours—about the same travel time as by road. The airport in Siem Reap has service to Phnom Penh and regular flights abroad to Thailand, Singapore, Vietnam, and Laos.

How to Visit

The fast-growing town of Siem Reap is the gateway to Angkor and is filled with lodging, dining, and tour-package options for all budgets and inclinations. Tour buses are available for those whose itineraries match what’s on offer—typically visits to Angkor’s major sites. Those interested in exploring more remote and off-the-beaten-track structures may hire cars or motorbikes with drivers and/or guides who are also able to suggest itineraries. Tethered balloon rides offer a unique aerial perspective from which to view the grand design of the Angkor complex.

When to Visit