The architecture of Wat San Paulo showcases a blend of Western and Eastern artistic styles, featuring an octagonal tower inspired by the Paris Observatory. Its robust brick-and-plaster walls employ French engineering principles to support the substantial weight of astronomical instruments. The design incorporates arched windows and doorways, hallmarks of European architecture, integrated with local Siamese materials and craftsmanship. The building's layout, divided into a chapel and an observatory, reflects a focus on scientific functionality in line with international standards of the time. As one of Lopburi's most significant historical sites, it exemplifies the advancement and assimilation of European civilization.