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 a foolery with a twist of 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://clevercreating.com/2018-06-20/.