Phra Thinang Kraisorn Siharat, or Phra Thinang Yen, is a single-story masonry pavilion with a cross-shaped plan located in Thale Chup Son. It boasts a unique architectural fusion, featuring distinctive pointed arch windows, a signature style from the reign of King Narai the Great. This site is globally significant as an observatory where the King used telescopes to observe a lunar eclipse with French astronomers. It marks the inception of Western scientific adoption and stands as a symbol of Thailand's modern astronomical advancement. Today, the ruins stand majestically, reflecting the progressive vision and historical international relations of ancient Lopburi.