Heat the oven to 350°F and grease a 9 x 13-inch baking pan. Prepare the cake mix with 1 cup water, 1/2 cup vegetable oil, and 3 large eggs according to the package directions.

Pour the batter into the prepared pan and bake for 25-30 minutes. The cake is ready when a toothpick inserted in the center comes out clean.

Cool the cake for about 20 minutes, until it is warm rather than hot. Use the handle of a wooden spoon, a large drinking straw, or a fork to make holes about 1 inch apart across the cake.

Dissolve the 3-ounce package of gelatin in 1 cup boiling water, stirring until completely dissolved. Stir in 1/2 cup cold water.

Slowly pour the gelatin mixture over the cake, concentrating on the holes so it can soak into the crumb. Pour gradually to help prevent excess liquid from pooling on the surface.

Refrigerate the cake for at least 1-2 hours, or until thoroughly chilled. Spread the thawed 8-ounce container of whipped topping over the cold cake.

Add fresh berries, sliced fruit, or sprinkles if desired. Cut the cake into squares and serve cold.