I was fascinated as a kid from various types of sailor knots. I was in the air modelling, then computer club, and our neighbours were the young sailors, but I've never got into it.

But I know kids around me were fascinated by them too (it could be that we were after all living in a fishing/sea town with lots of big ships, etc.).

But then even for girls (knitting, or other activities) - there is something about graph theory to be found there. Just wondering...