Most people are familiar with Shel Silverstein's poem "Where the Sidewalk Ends", but do they know where and why sidewalks crack? It's a valid and worthy question, and this handy educational activity from Charles Onasch of Bowling Green State University explains just that. Here, students will learn to use fractures in sidewalks as an analog for natural outcrops and also learn how to make systematic observations of such fractures. This activity is offered as part of the "Teaching Structural Geology in the 21st Century" website maintained at Carleton College, and educators are welcome to use it in a variety of classroom settings. Visitors can read a brief summary of the activity, and then go on to download all of the necessary documentation related to the activity.