The Harz Narrow Gauge Railways is a railway company that operates a meter gauge network in the Harz mountains, in central Germany. 

The company was formed after the Second World War as a merger of two earlier companies. It owns about 140 kilometers of the track, connecting the principal towns of Wernigerode, Nordhausen, and Quedlinburg and several smaller settlements in the area. 

Much of the network is steeply graded and picturesque, but its most popular destination is the Brocken, the highest mountain in the region. The company runs a significant number of its trains with steam haulage, mostly employing 1950s vintage 2-10-2 tank locomotives, hauling traditional open-platform bogie carriages. 

Source: https://en.wikipedia.org/wiki/Harz_Narrow_Gauge_Railways

BMX (bicycle motocross) bikes appeared in the early 1970s as an offshoot of motocross. They were designed for racing on dirt tracks replete with tight turns, berms, and jumps. BMX bikes are durable, with 20-inch- (51-cm-) diameter wheels mounted on a small frame. There is a single speed, the seat is low, and the handlebars are high. These traits make the BMX an extremely maneuverable bike, and it moved off the tracks and became popular on suburban and city streets. BMX-type bikes are used for freestyle riding, which emphasizes acrobatics rather than racing. 

Source: Berto, F. J. (2021, February 28). Bicycle. Encyclopedia Britannica. https://www.britannica.com/technology/bicycle