A Unesco World Heritage Site, this park features the ruins of structures dating back to the 14th century, roughly the same time as the better-known kingdom of Sukhothai. Kamphaeng Phet's Buddhist monuments continued to be built until the Ayuthaya period, nearly 200 years later, and thus possess elements of both Sukhothai and Ayuthaya styles, resulting in a school of Buddhist art quite unlike anywhere else in Thailand.

The park has two distinct parts; an inclusive ticket (150B) allows entry to both areas. The old city is surrounded by a wall (the 'Diamond Gate' of the city's name) and was formerly inhabited by monks of the gamavasi ('living in the community') sect. This area is dominated by Wat Phra Kaew, which used to be adjacent to the royal palace (now in ruins). It's not nearly as well restored as Sukhothai, but it's smaller, more intimate and less visited. Weather-corroded Buddha statues have assumed slender, porous forms that remind some visitors of the sculptures of Alberto Giacometti. About 100m southeast of Wat Phra Kaew is Wat Phra That, distinguished by a large round-based chedi surrounded by columns.

The majority of Kamphaeng Phet's ruins are found about 1.5km north of the city walls in an area previously home to monks of the arani ('living in forests') sect (admission 100B). An inclusive ticket purchased at the old city also allows entrance here, and there is an excellent visitor centre at the entrance. There are more than 40 temple compounds in this area, including Wat Phra Si Iriyabot, which has the shattered remains of standing, sitting, walking and reclining Buddha images all sculpted in the classic Sukhothai style.

Northwest of here, Wat Chang Rawp (Elephant-Encircled Temple) is just that – a temple with an elephant-buttressed wall. Several other temple ruins – most of them not much more than flat brick foundations, with the occasional weather-worn Buddha image – can be found in the same general vicinity.