The Einstein Tower (German: "Einsteinturm") is an astrophysical observatory in the Albert Einstein Science Park in Potsdam, Germany built by architect Erich Mendelsohn. 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 1919 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 Leibniz Institute for Astrophysics Potsdam. Light from the telescope is directed down through the shaft to the basement where the instruments and laboratory are located. There were more than half a dozen telescopes in the laboratory.