Patience and a well-developed sense of balance are required to be able to build these cairns. However, the question here is: What do these cairns do at the beach, and why four?
The problem lies with us. We think cairns are only erected to mark directions. But wiki-something says they are also set up for defense, hunting, or ceremonial purposes, or to locate buried items. We didn’t look underneath.
In this case, we think it’s just foolery with a twist of a challenge because of the patience and balance that are required.
Remarkable as it might seem, in this virtual age a completely new kind of cairns has been developed. Go to the website what3words.com and you will understand. Or read this guestblog: https://nogeraniums.com/2018-06-20/.