The state museum for technology and labour in Baden-Württemberg, housed in a former tram depot. The permanent exhibition covers the industrial history of the Rhine-Neckar region with actual machines — steam engines, printing presses, early automobiles — in working condition. A replica of Karl Benz's 1885 Patent Motorwagen sits here; the original is in the Deutsche Museum in Munich, but this gives a sense of how modest the first petrol car actually was.
The museum leans into hands-on interaction, which makes it genuinely good for children, but the depth of content means adults get plenty too. Allow two to three hours.