The "Schlossgartenbahn" is a small 600mm narrow gauge park-railway running in the park of the castle in Karlsruhe. It was built in 1967 for the "Bundesgartenschau" and is still running during summer. From the original trains, only the "Porschelog" is active (again). But there are two other engines: one steamer and a Diesel. (More information and images can be found on this german wikipedia page)
Years ago I built the railway in a rather large scale. In the meantime circuit cubes and trixbrix tracks became available and so I did it again in mini-figure scale.
coupling rods are from bricks-on-rails.de
Both trains are powered by a circuit cubes motor - the receiver/battery is "hidden" in the first coach. Additional weight is needed to get enough traction to move the coaches with the small LEGO wheels. They do no run a smooth as standard LEGO train wheels.
I tried to hide the wheels of the coaches completely to have the same look as the original.
Video of both trains - they both handle R24(!) curves.
Last summer I tested the steam train on "rough terrain":