Old Synagogue, Religious building in Dortmund, Germany.

The Old Synagogue was a synagogue on Hiltropwall in Dortmund, completed in 1900 and demolished in 1938. Designed by Eduard Fürstenau in a neo-Gothic style, it seated 1,300 people, with 750 places for men on the ground floor and 450 for women on the galleries of the dome. Its interior decoration was by August Oetken, and its Walcker organ had 40 registers. The site is now occupied by the Dortmund Opera House.

The community's first prayer house stood at Wüstenhof; by 1870 it had over 2,000 members, prompting a larger building. A site at Hiltropwall was bought, and Eduard Fürstenau won the architectural competition with a neo-Gothic design modelled on the opposite Oberpostdirektion. The synagogue opened on 8 June 1900 with 1,300 seats. In 1938 the Nazi city leadership forced the sale, seized the proceeds, and demolition began on 18 October, finishing in December 1938.

The synagogue's name lives on in the Platz der Alten Synagoge, the forecourt of the Dortmund theatre, officially named in 1998. A memorial stone and a plaque about 120 by 60 centimetres commemorate the building demolished in 1938. The organ, built by E. F. Walcker & Cie. in 1900 with three manuals, pedal and 40 registers, stood on the singers' gallery above the Torah shrine.

The synagogue no longer exists: it was demolished in December 1938, and the Opernhaus Dortmund has stood on the Hiltropwall site since 1958–1965. What remains is the forecourt, officially named Platz der Alten Synagoge since 1998, with a memorial stone and a plaque about 120 × 60 cm. Look for them in front of the theatre.

The synagogue had a Walcker organ from 1900 with three manuals, a pedal and 40 registers, enlarged in 1907 with a ten-register Fernwerk. Organists included Carl Holtschneider and, from 1930, Gerard Bunk, who also played at St. Reinoldi. The gilded ball on the dome was removed on 21 September 1938 during a staged ceremony.