Sandbox

FIG. 1 is a perspective view of a sandbox showing my new design; FIG. 2 is another perspective view thereof; FIG. 3 is a front view thereof; FIG. 4 is a back view thereof; FIG. 5 is a left view thereof; FIG. 6 is a right view thereof; FIG. 7 is a top plan view thereof; and, FIG. 8 is a bottom plan view thereof. The broken lines depict portions of the sandbox and form no part of the claimed design.