Koh Ker is an Angkorian site in northern Cambodia. 100 km northeast of Angkor itself, it was briefly the capital of the Khmer empire between 928 and 944 under king Jayavarman IV and his son Hasavarman II.
Here a vast number of temples were built under his reign, until his successor returned to the Angkor area about twenty years later.

Most visitors start at Prasat Krahom (Red Temple), the second-largest structure at Koh Ker, which is named for the red bricks from which it is constructed. Sadly, none of the carved lions for which this temple was once known remain, though there’s still plenty to see – stone archways and galleries lean hither and thither and impressive stone carvings grace lintels, doorposts and slender window columns. A naga-flanked causeway and series of sanctuaries, libraries and gates lead past trees and vegetation-covered ponds. Just west of Prasat Krahom, at the far end of a half-fallen colonnade, are the remains of an impressive statue of Nandin.

The Koh Ker site is dominated by Prasat Thom, a 30 meter tall temple mountain raising high above the plain and the surrounding forest. Great views await the visitor at the end of an adventurous climb.
The principal monument is about 55m-wide, 40m-high sandstone-faced pyramid with seven tiers that's just west of Prasat Krahom. This striking structure, which looks like it could almost be a Mayan site somewhere on the Yucatan Peninsula, offers some spectacular views across the forest from its summit. Look out for the giant garuda under the collapsed chamber at the top of the vertigo-inducing stairs. Some 40 inscriptions, dating from 932 to 1010, have been found at Prasat Thom.