Prasat Phimai is one of the most impressive Khmer ruins in Thailand, both in its grand scale and its intricate details. Though built as a Mahayana Buddhist temple, its carvings feature many Hindu deities, and many design elements – most notably the main shrine's distinctive prang tower – were later used at Angkor Wat. There has been a temple at this naturally fortified site since at least the 8th century, though most of the existing buildings were erected in the late 11th century by Khmer King Jayavarman VI.
You enter over a cruciform naga bridge, which symbolically represents the passage from earth to heaven, and then through the southern gate of the outer wall, which stretches 565m by 1030m. The orientation to the south (though not due south) is unusual since most Khmer temples face east. It's often written that Phimai was built facing south to align with the capital, though historians reject this theory since it doesn't face Angkor directly.
A raised passageway, formerly covered by a tiled roof, leads to the inner sanctum and the 28m-tall main shrine built of white sandstone and covered in superb carvings. Inside the adjacent Prang Brahmathat is a replica stone sculpture of Angkor King Jayavarman VII, sitting cross-legged and looking very much like a sitting Buddha. The original is in the Phimai National Museum.
Knowledgeable local students sometimes act as guides, but few speak English. Luckily, various signs and a free brochure from the visitors centre just inside the entrance provide a decent overview of the complex.