Does this remind anyone else of the Old Testament fathers who built altars of stone?
He got up early the next morning and built an altar at the foot of the mountain and set up twelve stone pillars representing the twelve tribes of Israel. (from Exodus 24)
Wherever something significant happened, they built an altar from stones. Maybe this is where the Irish Christian pilgrims got the idea. But then again, pre-Christian Celts built stone cairns as well.
It's something to think about the next time you are on a hiking trail and add a stone to a pile you see. What journey are you on and how will you mark your encounter with your Maker? You might not use a physical marker but everyone has turning points. What do you think?