My daughter started sailing last summer, and came home each day to show us a new knot she learned. She had so much fun experimenting with different types of knots: cleats, figure 8, the bowline. Fortunately, I found a free knot tying workshop at the local library, run by the Cape Cod Maritime Museum.
She and her brother had so much fun exploring those knots and learning more. We even learned the monkey's fist knot!
I bought scraps of rope at our local hardware, and we keep it in the car - this is a great activity for travel!