You can get to the sand pit by parking in the main parking lot and heading toward the rose gardens. Pass over the bridge and make a right. You'll see the sand pit when the road turns left. It's not actually on the map, as it isn't a garden itself. This spot in the gardens is one of the shortest walks, and it's perfect for a quick weekday afternoon stop or the first stop on a full morning trek.
Whenever people ask me which local membership is the best deal, I never hesitate to say Botanical Gardens. Their two year membership is $165.00. This seems like a lot, but it lasts two years, and it gets in six people in every visit. Unlike many of the memberships, this one doesn't have names on it, so you can bring in different people whenever you come. It also gets you discounts on special events like Latern Asia, the Million Bulb Walk, and the Garden of Lights. It also gets you discounts on classes that they have in the gardens