In this activity about saturation (page 1 of PDF under SciGirls Activity: Sand Dunes), learners will build a series of sand castle towers using a 16 oz cup. Learners begin with completely dry sand and then add a ΒΌ cup of water to the sand for each successive tower, each time measuring the height and width of the resulting sand mound until they make a tower that maintains the shape of the cup. Relates to the linked video, DragonflyTV: Sand Dunes.