I would like to know what "wade through its lunar landscape" means in the following sentences:
In the afternoons we were free. Beniek and I and some other boys would go to the beach and swim in the cold and turbulent Baltic. Afterwards, he and I would dry off and leave the others. We’d climb the dunes of the beach and wade through its lunar landscape until we found a perfect crest: high and hidden like the crater of a dormant volcano. There we’d curl up like tired storks after a sea crossing and fall asleep with the kind summer wind on our backs.
In this novel which is set in the 1980's in Poland under the socialist regime, where homosexuality was socially unacceptable, the protagonist Ludwik (a university graduate) left Poland in 1981 to live in the United States of America. And he remembers what it was like back then in Poland, where he used to hang out with his friends including his first love Beniek in his hometown of Wrocław when he was nine years old. He also went to a trip for his First Communion, where he used to swim and "wade through" the "lunar landscape" on the beach with Beniek.
In this part, I wonder whether "its lunar landscape" means the the crescent form of sand dunes on the beach, or the beach's landscape on which moonlight shone. But, it was only afternoon when children swam in the ocean, so I believe it was not dark enough for the moon to shine, though it says "lunar"... so I am confused and wanted to ask you.
I am an English learner from South Korea. I would very much appreciate your help. :)