A sandy area which starts with an s would be a shoal.
The Sahara, the world's largest desert.
A sandy area is a beach!
Beach.
sameness sanctimonious scandalous salacious seamless senseless straightness serious serendipitous singleness sinfulness smokeless surpass sneakiness sepsis shortness spacious spyglass stainless...
So many things start with S, like songs, and sons, and stories, and steaks; even this sentence starts with S.