Final answer:
The Boston Sand Garden was notable for introducing the first sandbox to a playground, marking an important development in children's play areas.
Step-by-step explanation:
The Boston Sand Garden was a unique playground facility because it was the first to have a sandbox.
Historically, the introduction of sandboxes to play areas was a significant innovation. The Boston Sand Garden, which came into existence in the late 19th century, was a pioneer in recognizing the play needs of children. This innovation provided a dedicated space for creative and tactile play, which was important for child development.
While Gardens by the Bay and other facilities, like Fenway Park, provided leisure and green spaces for adults and families, the Boston Sand Garden focused on the play aspect specifically for children, bringing the benefits of outdoor play into the urban environment.