In the 18th century Leonhard Euler famously addressed the question whether it was possible to walk through the city of Königsberg and return to one’s home having crossed each of seven bridges exactly once.
The answer, briefly, was no, but in 2013 network scientist Thilo Gross noticed that the city of Bristol has a similar layout, and here the task is possible: If you’re willing to walk 30 miles, you can cross each of the 45 bridges on this map and return to your starting point.