Arizona's 20-20 Challenge is a web site for hikers, created for the Arizona Office of Tourism. The web site lists the 20 highest summit trails and the 20 deepest canyon trails of Arizona, and provides maps and information for each. The Challenge offers a southwestern twist on the increasingly popular concept of 'peak bagging', which is extended here for the first time to canyons. Developing the list proved to be more challenging than expected, in part because of the difficulty of determining what qualifies as a summit or canyon, whether the summit or canyon is independent of its neighbours and whether an open trail exists. Recreational, cultural and environmental factors were taken into account in addition to geo morphological criteria. The design and content of the web site is described and compared to other peak-bagging sites, which vary greatly in their emphases. Two such web sites, for Scotland and the Adirondacks, indicate that peak-baggers have completed at least 800,000 hikes in the two regions combined and that the activity is accelerating in popularity.