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.
It probably isn't the best use of the city's funds, but given the specific geography of the city, using the space above the river that runs along the entire narrow valley that makes up most of Wuppertal, it does make some sense.
Seattle has a weird suspension monorail but it literally only goes a few blocks. I lived there for years and never knew anyone who ever took it it was so useless!
