The aim is to move a whole pile of rods, but in a certain way. Bigger rods can never be on top of smaller ones. You can only move the top rod in the pile. You can never put a big rod on top of a small one. You can only have one pile in a circle.
The challenge was, not just to do the puzzle, but to be able to find a way to write down what we had done. We found lots of different ways:
Some of us shared our ways with the whole class.
It was interesting to look at the pattern in the minimum number of moves necessary for different sized piles of rods at the start:
PS The next day Rod brought in his own Towers of Hanoi: