You have Phanom Rung and Prasat Hin Muang Tam.
Google both.
Phanom Rung is about 12 km south of the 24 road Nang Rong and Prakhonchai. I suggest sat nav if you are taking the direct route of 331, 359, 33, 3395, 348 etc via Wattana Nakhon, Lahansai...
The tidiest route is No 7 road and take the Chachoengsao turn just after the big rest area. After driving for about 20km you take the right lane to turn towards Kabin Buri. This road eventually merges with the 331and you then take a left exit to Sa Keaw on the 359..