How long is Britain's coastline? Honestly, the question doesn't really have an answer
Measure a coastline with a 100 km ruler, then a 1 km ruler, then a 1 m ruler, tracing every inlet and headland the shorter ruler can reach that the longer one skipped. What happens to the total length as the ruler keeps shrinking: does it converge on a true number, or does something stranger happen?
Reveal the answer
The measured length keeps increasing without settling on a fixed number, because coastlines are fractal-like: they contain detail at every scale, so a finer ruler always finds more wiggles to add. Lewis Fry Richardson first observed this in the 1950s, and Benoit Mandelbrot formalized it in his famous 1967 paper 'How Long Is the Coast of Britain?', helping to launch the mathematics of fractals.