This grand building, founded in 1810 as the university's original observatory, now serves as one of the university's museum branches. The Old Observatory, being Estonia's first, marks the beginning of local astronomy. Its exhibitions chronicle the history of astronomy in Estonia and globally, spanning from the early 19th century to the era of the Soviet space program. Visitors can explore antique stargazing devices, engage with interactive exhibits, and enjoy city views from outside. Friedrich Wilhelm Struve, its most renowned director (from 1820 to 1839), installed the most powerful telescope of that era. A prominent plaque outside honors Struve's Geodetic Arc, a chain of survey triangulations extending 2,820 km from Norway to the Black Sea, which was added to UNESCO's Cultural Heritage List in 2005.