From the longer German Wikipedia page [1]

The City Archives Dortmund is the municipal archive of the City of Dortmund, Germany.

The municipal archive includes both the memorial and memorial site Steinwache, the central memorial site to the Nazi crimes in Dortmund, as well as the office of the Historical Association for Dortmund and the County of Mark. The archive has some archaeological finds dating back to the 13th century, which are now preserved in the Museum of Art and Cultural History of the city.

The use of the city archives is possible for all interested parties. The basis for the work of the Stadtarchiv is the Archivgesetz Nordrhein-Westfalen. Through the continuous takeover of municipal files and private estates, documents of churches, parties and companies as well as collections of photos and graphics, films, maps, the archive stocks are growing.

The website is [2].