Take a day to visit the Ayutthaya Historical Park; it is around 60 miles North of Bangkok. It is now the UNESCO World Heritage Site, with some of the area still in ruins but several of the Buddhist temples (Wats) can be found on foot because they are so close to each other. Among the ones you should be looking for are:
Wat Na Phra Meru
Wat Mongkhon Bophit
Wat Phra Si Sanphet (the largest one)
HI
Guide Tour Travel Thailand Other..
Thank you.