It is known that all functions that are continuous and nowhere differentiable are also nowhere monotone but that there is a function that is everywhere differentiable but nowhere monotone. I have looked at one such construction but it was involved and I didn't manage to get a feel or an intuition for how it is possible to oscillate so much that you are nowhere monotone but still be well-behaved enough to be differentiable everywhere.
I guess that I am asking if anyone can explain the intuition/key idea behind those constructions.