Phra Thinang Yen, officially named "Phra Thinang Kraisorn Siharat", was built by King Narai the Great in Thale Chup Son as a summer retreat. Its architecture showcases a masonry style influenced by Persian and European designs, featuring distinctive and beautiful pointed arch windows. This site holds global historical significance as the location where King Narai observed a lunar eclipse using a telescope. This observation, conducted alongside French Jesuit astronomers, is considered the first step of modern astronomy in Siam. Today, even though only the walls and brick structures remain, the peaceful atmosphere continues to attract visitors to experience the past.