Sand Gardens

"There are two main historical antecedents for the modern conception of the playground, and they both come from Germany. One was the creation of sand gardens (see also A Brief History of the Sandbox).  In the late 19th century, piles of sand were dumped in public parks as an antidote to the delinquency of street urchins, in hopes of giving them something to do other than bother the keepers and customers of the shops that surrounded the parks."

source play-scapes.com