In the location's words:

The Archenhold Observatory in Treptower Park is the largest and oldest public observatory in Germany. Its focal point is the giant telescope built in 1896, with a focal length of 21 meters the longest movable refracting telescope in the world. Other attractions include the historic Einstein Hall (where Albert Einstein spoke publicly about the theory of relativity for the first time), Berlin's largest meteorite and the "Museum of Celestial Science". The public observations, for example at the "Night at the Observatory", are popular at any time of year, and children can take part in "We build and launch water rockets", a "Visit to the Star House" or a "Journey to the Moon".