Pom Phet or Diamond Castle was one of the sixteen castles along the city walls of Ayutthaya, located in the southeast of the city, at the confluence of the Pak Sak and Chao Phraya rivers in the Bang Kai district and on the east bank of the Nai Kai Canal. This castle used to protect the harbour, but today it is an ideal public park for laying on the green grass and taking pleasant strolls by the river.