The huge temple directly across the road from the railway station is, according to some, the oldest Buddhist temple in Lopburi. There's actually some controversy about the age of the temple. The 'official' line is that the central tower (prang) dates from the twelfth century, but some have argued that the lines of the tower are more in keeping with later styles of the early Ayutthaya era. As with most Thai temples, Wat Phra Sri Rattana Mahathat was constantly renovated, restored and 'modernized' as the times changed.
What everyone does agree on is that the temple was extensively renovated and expanded under King Narai in the seventeenth century. The large prayer hall on the east of the central tower was added, as were many of the smaller prangs and chedis around the complex.
The size of the temple is impressive in itself, and if you look closely at the towers, you will find some exquisite details still intact here and there.
Wat Phra Sri Rattana Mahathat is open daily and carries an admission fee of 50 Baht (1.30 USD).