The Bad Piggies Sand-Box levels are awesome! There are currently only 5 available and you have to complete (get 3 stars on) all the levels for a theme or section to unlock them. Two Sand-Box levels are unlocked after completing the 36 original levels of Ground Hog Day and When Pigs Fly. Two more are unlocked when you get three stars on the 9 bonus levels of each of these themes. Finally, the Bad Piggies Sandbox S-5 level is unlocked once you complete the Find The Skulls challenge. Unlike other episodes of Bad Piggies, the Sandbox levels have 20 hidden stars. You can take multiple turns to find them all. Some Sand-Box levels require you to build multiple contraptions, as well. Below are the Sandbox Walkthrough videos for each level.