I got the image off of an almost impossible to search Russian site https://ok.ru
I cannot the image again so as to find out where in the world it is :~(
But you're right - it is very relaxing :~)
I remember in the 1970's you could buy a 'Rock Tumbling Machine' and you left it running for weeks to achieve the same result as the picture - who knew you could go to that beach (where ever it is ?) and pick 'em up ! :~)