I once spent a night in Wuppertal just to ride this thing. Rode it from end to end, and then again the next morning. What was unexpected was how modern it is. You might expect a rickety historic tourist contraption, but in fact it's a modern metro with great views and an unusual ride.

As I understand it, in most countries the railway would be completely uneconomical since it has no off-the-shelf parts and there are no tourists in Wuppertal, but in Germany it makes some sense since it can be used as a sort of training bed for local engineering students and industry.