EL-DE Haus, Nazi documentation center in Altstadt-Nord, Germany.

EL-DE Haus is a five-storey corner building at Appellhofplatz 23–25, faced in light tan ashlar with rusticated stone wrapping the corner edge. Rows of rectangular windows with dark frames run across the facade, some upper sills carrying green metal railings. A projecting cornice separates the top storey, and a carved stone relief is mounted on the corner.

From 1935 to 1945, the building served as headquarters for the Cologne Gestapo with interrogation rooms and prison cells in the basement. The period under secret police control left deep scars on the city's history.

The name comes from the initials of gold and watch wholesaler Leopold Dahmen, who had the corner relief carved with his mark: two crossed clock hands with the letters L and D. Since 1988 the building has housed the NS Documentation Centre of the City of Cologne, and the cellar cells with prisoners' wall inscriptions can be visited.

The cellar prison lies below street level and is reached by two steep stairways secured with iron grilles; the main entrance is on Appellhofplatz, the side entrance on Elisenstraße. The building stands at Appellhofplatz 23–25, corner of Elisenstraße, near the courthouse and the former police headquarters in Krebsgasse.

The basement rooms contain over 1800 inscriptions that prisoners carved into the walls during their captivity. These markings form direct testimonies of personal experiences from a time of extreme oppression.