One of several NS-Dokumentationszentrum dotted all over Germany with other notable ones in Nürnberg and Munich, it displays the history of the Third Reich and Germany’s dark Nazi past in Köln. The EL DE Haus itself was a former Gestapo headquarter with torture chambers and prison cells in the basement of the building. Many of its cells still have messages inscribed on the wall by its many prisoners in the past, some of it in languages of Allied spies.
Though many have been tortured here, some have been executed or tortured to death. There’s really no excuse for this kind of behaviour so the museum as preserved many of its artefacts in a sensitively curated manner upstairs. Much of it is in German so I do recommend either the English audioguide or picking up a multilingual leaflet at the main entrance.
It is one of only two German museums to have won the Best in Heritage award for museums. There is a small library of books about the Third Reich available for research purposes. Entry is free, but I do recommend donating a Euro or two so they can keep educating future generations about the horrors of war.