San Paulo Temple was once a Jesuit church and an astronomical observatory established by French priests during King Narai's reign. Its architecture featured a prominent three-story octagonal tower, which was used for telescopic observations of the stars. The building was clearly influenced by Western design, reflecting the scientific and astronomical prosperity of Lopburi's golden age. Today, only the brick walls and tower foundations remain as vital evidence of the knowledge exchange between Siam and Europe. This site is considered the first international-standard astronomical observatory in Southeast Asia to record celestial phenomena.