@mwichary if you find yourself in NW Germany:
- Universeum Bremen
- Klimahaus Bremerhaven
- Miniatur Wunderland Hamburg
Near Stuttgart is the Museumsstellwerk Calw, on my list of places to visit. Or any other Museumsstellwerk.
If you go to Essen, also consider
- Landschaftspark Duisburg-Nord
- Magic Mountain (a coal spoil heap featured in a Tom Scott video)
Anti-recommendation: Technikmuseum Berlin. It’s just… meh.