I'm quite fascinated by the concept of a desire path, in Dutch called olifantenpad (elephant path). They're humanly made trails caused by human (or animal) movement. It's a route, not planned as such, but created because it's a more convenient way to get somewhere. Usually they emerge as shortcuts where constructed roads or footpaths take a longer route.
At the Technical University of Eindhoven there's an example called the "Limbopad": the shortest way through the grass between the main university building and the train station. It's named this way because students from Limburg had to take the first train back home. It has now become an official path, but the name stuck.
Desire paths can be a good guideline for planning new trails and urban planning of new road networks.
The term olifantenpad has also now become a metaphor for more intuitive design choices, anarchism or the way users bypass limitations in software: solutions that, over time, are followed by an increasing number of people. One example of this is the use of hashtags on social media: as more and more people began using them, the hashtag was eventually integrated as an official feature.