Abstract: A flat, collapsible blank which is assembled to form a box of suitable thickness and sufficient rigidity. Four panels of the same size and shape are hinged serially. Each has folding end flaps with diagonally opposed tabs and opposing bevelled corners. Further, each end flap has a slot situated such that it cooperates with and is joined by the tab on the end flap of the adjacent panel. Hence, the interlocking box has interlapping end flaps which when taken together form the top and bottom panels of the box. Additionally, each corner tab has a meshed area on the exterior surface thereof, and each slot has a meshed area on the interior surface thereof, such that the two meshed areas cooperate. These meshed areas are used to add rigidity and support to the top and bottom panels when each end flap is folded in its configuration during use. The box can also be used by children as a toy or plaything, being large enough for them to climb into.