The Magic Cube is a rare artifact that, other than conferring some enviable radiation and physical protection stats, will also net you a cool 30,000 coupons as part of the A Job for the Barkeep ...
but you will find the real loot inside the secret cave, whose door is in the middle of two turtle statues. To open the secret Magic Mosses Cave door in Fortnite, saying “Open Sesame!” ...