Or also called Phi Mai Historical Park is located right in the middle of the modern town of Phi Mai and it about 60 km north of Khorat (Nakhon Rachtasima). Just follow route 2 in direction of Nong Khai and 50 km after Khorat you take rout 206 to Phi Mai. See location tag.
It is one of Thailand's most important Khmer temples build in the 11th - 12th century. It is easy to visit as it is first of all easy to reach (there is even public transport from Khorat going to Phi Mai) and secondly it is build in a easy to walk terrain. Opposite the entrance is also a nice air conditioned coffee-shop and of course some souvenirs shops. When you enter the park you see the entrance on your left hand side (and on your right hand side toilets) with the Naga bridge. Walking to the rear side of the park you will have a beautiful view over the complex and see the main Prang surrounded by the smaller Prang's.
The complex is build in perfect symmetry which gives you a beautiful view when looking trough the doors. Of course the Buddha image (protected by the Naga) is not the original. On many places you will see beautiful wall reliefs like this one, most times above doors to bless all entering the building.