On Kasem Road, Wat Mahathat has a spectacular 42-metre-tall central white prang, which can be seen from much of town.
Believed to have been built around 800 years ago, the temple shows considerable Khmer influence and marks pretty much the southern limit of the Khmer empire at its grandest. The central prang is floodlit in the evening, making it doubly impressive. The main bot contains some interesting murals -- keep an eye out for the people mooning one another!
You'll find Wat Yai Suwannaram towards the eastern end of town on Phongsuriya Road. It's been renovated on a number of occasions and is best known for its Ayutthaya-period murals, a couple of very old and ornate wooden doors, and the teak buildings that have impressively borne out time. The pond in the centre of the area hides large sacred fish and turtles in its decidedly green waters.
Around the corner from Wat Yai Suwannaram on Pho Karong Road, the modern Wat Kamphaeng Laeng is of no interest, but the ruined and original sandstone site is worth a quick look. Parts of the original wall which date to the 13th century still remain from when it was originally a Khmer religious site.
Take the southern entrance out of Wat Kamphaeng Laeng, turn right and follow Phrasong Road -- you'll eventually reach Wat Phailom. As with Wat Kamphaeng Laeng, the modern temple is of little interest, but there is a ruined wat here that's noteworthy for the remnants of its stucco work, especially on the back wall.
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