Wat Mahathat Worawiharn
The five towers (prangs) of this temple's main pagoda can be seen from all over town. The temple's origins are believed to go as far back as the twelfth century, when the Khmers ruled the entire region through their vassal state Lopburi.
The pagoda is enclosed by a small gallery, and seems to be closed to the public. On the east side of the enclosure is the temple's main prayer hall. This is definitely worth a look inside. The walls of the hall are covered with murals, which appear to date from the Ayutthaya period. There are depictions of early westerners that visited Siam, as well as some 'interesting' battle scenes.
Next to the prayer hall is a small pavilion sheltering a Buddha image. The next chapel over is the temple's ordination hall. Unlike the prayer hall, the ordination chapel is relatively plain.