It was conceived in the late 1890s as an innovative transport solution for a developing group of townships then springing up along the River Wupper, in the industrial heartland of North Rhine-Westphalia, Germany.
These towns eventually merged to form the city of Wuppertal in 1930.
The river snaked its way through a narrow valley, and space was already at a premium, so the solution was to build the electric railway following the course of the river, suspended above it.
It opened in 1901, and remains in operation today, as the oldest monorail system in the world, albeit extensively modernised between 1997 and 2004.
It is just over 13km long, suspended 12 meters above the River Wupper, and 8 meters above the city streets. Each working day, 82,000 passengers are carried between its 20 stations in 27 articulated twin units.
I knew none of this when, on my visit to Germany in April 2008, my German friends took me to see it.
On Saturday 12th April, we made the journey to Wuppertal, and my first sight of this railway just took my breath away. A giant steel colossus snaking its way between modern buildings and over city streets.
It reminded me immediately of the railway in the classic 1927 Fritz Lang film 'Metropolis', perhaps more readily known today, as featured in the 1980s Queen video for their hit single Radio Gaga. I had absolutely no idea that such a railway actually existed!
We had time to take a short ride, which was an experience in itself.
Standing on a station platform looking down to see no track in situ was strange, and a walk to the platform end revealed a sheer drop into the river below.
Leaving the confines of the station and finding yourself way over the river for the first time was quite unnerving, as was disembarkation.
When the train stopped, the carriage swung gently from side to side, so stepping off onto the platform was akin to stepping off an escalator back onto terra firma.
Here are some photos of this remarkable railway: