Wat Prasat, or the Monastery of the Castle, was located on Ayutthaya's city island in the western part of the city in the Pratu Chai Sub-district.

The site is only indicated on a 19th-century map by an unknown surveyor and does not feature on Phraya Boran Rachathanin's (PBR) map drafted in 1926 CE, which shows only empty space in that area.

The monastery was situated on the south bank of a minor canal or ditch longing the Lao Road. In the east stood Wat Saek, while on its south stood Wat Jom Thong. The 19th-century map indicates the presence of a prang.

There are no traces anymore visible of the monastery above ground level. I presume this area was already cleared of temple ruins before Phraya Boran Rachathanin arrived in Ayutthaya.

Historical data about the monastery and its construction are unknown.

Wat Prasat must have been located in approximative geographical coordinates: 14° 21' 1.08" N, 100° 33' 0.84" E.