In the Dieringhausen district of Gummersbach, the Dieringhausen Railway Museum forms a central point of reference for the transport history of the Oberbergisches Land. The museum occupies the 11,000 m² site of the former Bahnbetriebswerk Dieringhausen and is listed as a technical ensemble.
The facility developed from a locomotive site established in 1893; with the expansion of the regional rail network a Bahnbetriebswerk was set up in 1905, which grew structurally and functionally in the following decades. In 1920 the Aggertalbahn was rerouted and the new station was built about 500 metres to the north; the depot remained accessible via a branch line. Air raids in the Second World War destroyed parts of the facility in 1944; reconstruction took place as early as 1945. Subsequently, railbuses (from 1956) and diesel locomotives (from 1962) entered the fleet; with the farewell to steam locomotives in 1969 the era of steam traction came to an end. Because of network reductions, Deutsche Bundesbahn closed the depot on 30 April 1982.
The museum use began in 1982, when a regional association developed the site for the purpose of a railway museum and an operating company was founded. A patron purchased the site from Deutsche Bundesbahn and thus enabled the collection and restoration of numerous historic vehicles. After financial crises and a temporary closure in 2009, integration into the Hermann-Haeck-Stiftung was achieved at the end of 2009; museum operations were resumed. Until April 2021 the museum and its vehicles belonged to the foundation; since then the site and museum have been privately owned. The museum association operates under the name IG Bw Dieringhausen and continues to run the museum.
Significant exhibits include the steam locomotive "Waldbröl" of the Kleinbahn Bielstein–Waldbröl, which has been returned to service, as well as the last surviving Prussian T 14 in Germany, locomotive 93 230, on a 15-year long-term loan from the Verkehrsmuseum Dresden (since September 2010). Since 2007 the collection has been sharpened in favour of regionally typical vehicles; individual large vehicles have been sold or transferred.
Architecturally striking is the three-storey arrangement of the Bahnbetriebswerk: on the lower level are the roundhouse, turntable, inspection pits and locomotive servicing facilities; above them are coal bunkers and service rooms; at the very top are the tracks of the former goods yard and the alignment of the lines. The historic roundhouse from 1906 has eleven bays; the turntable measures 22 metres in diameter. The collection currently comprises eleven steam locomotives (two operational), seven diesel locomotives (three operational), a Uerdingen railbus, an electric locomotive and an extensive collection of passenger and freight wagons. A large portion of the vehicles belong to the Hermann-Haeck-Stiftung; others come from the museum association and private lenders.