Outstandingly beautiful! It is actually one of the reasons I took a trip to Bangkok in the first place. The ruins really takes you to the ancient times... still well maintained so that you could feel that you're in the different lifetime when visitiing..
The stone craft detail is just beautiful..
Words couldnt do it justice..
Three temples to be recommended: Wat Phra Si Sanpet, Wat Maha That and Wat Chai Wattanaram (the best!)