Lopburi city is also known as monkey town. It is only 155 km away from Bangkok on the east bank of the river Lopburi. A huge pack of monkeys has their own old temple in the city centre. The city of Lopburi was part of the ancient empires of the Dvaravati, Khmer, Sukhothai and Ayutthaya. The preserved ruins in the old part of town are remains of these episodes in history. In Lopburi Province there are huge sunflower fields. Lopburi city can be reached by train from Bangkok, Ayutthaya and Pak Chong (Khao Yai National Park).
Travel and background information.
See some nice pictures on Flickr.
Detailed information on www.wikitravel.org.
Travel information at www.thailandbytrain.com.