The Einstein Tower (German: Einsteinturm) is an astrophysical observatory in the Albert Einstein Science Park in Potsdam, Germany. It was built on the summit of the Potsdam Telegraphenberg to house a solar telescope designed by the astronomer Erwin Finlay-Freundlich. The telescope supports experiments and observations to validate (or disprove) Albert Einstein's relativity theory. The building was first conceived around 1917, built from 1920 to 1921 after a fund-raising drive, and became operational in 1924. Although Einstein never worked there, he supported the construction and operation of the telescope. It is still a working solar observatory today as part of the Astrophysical Institute Potsdam. Light from the telescope is brought down through the shaft to the basement where the instruments and laboratory are located. This was one of Mendelsohn's first major projects, completed when a young Richard Neutra was on his staff, and is his best-known building.