For Topping: Melt butter over low heat in 12-inch cast-iron skillet. Remove from heat. Stir in brown sugar. Spread to cover bottom of skillet. Arrange pineapple slices and maraschino cherries in skillet. Set aside.
For Cake: Combine cake mix, pudding mix, eggs, water and oil in large mixing bowl. Beat at medium speed with electric mixer for 2 minutes. Pour batter evenly over fruit in skillet.
Bake in 350 oven for 1 hour or until toothpick inserted in center comes out clean. Using oven mitts to handle pan, invert onto serving plate immediately after removing the cake from the oven.