Growing up in a dusty town in the middle of a land locked province, I haven’t spent terribly much of my life on beaches with sand that isn’t made up of cigarette butts and small rocks, but if I did live somewhere with sand, I’d be the crazy one out there doing this.
Much like the backyard sand casting enthusiasts the process is pretty simple: Take a bunch of soft metals and melt them down into a liquid. Make a mold out of sand, fill the hole with the hot metal and allow to cool relatively slowly (the faster you cool, the more likely it’ll warp and / or snap). Then, take the sand away.
Obviously you need some good volume of sand to be making stools in your backyard, and that’s where the beach really is ideal, but you can make lots of things in fairly low volume containers. Sand isn’t the best for tiny things though, if you’re planning on doing jewelry, definitely use waxes or composite molding materials for a smoother finish.