This temple is also settled on an extinct volcano like the Khmer temple of Phanom Rung
which is 20 km away. The construction of the Wat Khao Angkhan temple dates back from the Khmer period. The Dvaravati era (8th or 9th century) to be more precise. The main red building seen today is a reconstruction believed to date from the 1980s as the original was too much in ruins but many sandstone markers delimiting the area of a sacred temple have been found here and are from the Dvaravati period Khmer. The temple features buildings in various architectural styles. Inside the main building surrounded by a square of all different seated Buddhas, there are wall paintings of legends and stories of Buddhism in English. I couldn't get in because it was under renovation so I can't tell you more.
Also note the very recent 29 meters long reclining Buddha at the left of the main wiharn.