The Purple Mountain Observatory (紫金山天文台), established in 1934 on the summit of Purple Mountain, was China's first modern astronomical observatory. The hilltop position gives it panoramic views over Nanjing and the surrounding plain. The historic domed telescope buildings are preserved, and a museum covers the history of Chinese astronomy from ancient times to the modern era.
The observatory discovered several asteroids and minor planets, some of which are named after Chinese historical figures and scientists. The path up to the summit, through the forested upper slopes of Purple Mountain, is pleasant in itself — allow 30-40 minutes to walk up from the cable car station. Not a long visit, but the combination of the view and the institutional history is worth the detour.