Very large, high resolution, interactive screens—also known as interactive walls—can be used to deliver entertainment and advertising content that is qualitatively different from what is available in television, kiosk, or desktop formats. At a sufficient resolution and size, the touchable wall can offer the engaging interactivity of full-fledged entertainment software, but on a scale that enables new kinds of public experiences. This paper describes some of the opportunities enabled by what we believe to be a new computing medium in its own right. We also describe some of the new design challenges inherent in this medium, together with suggestions based on our own approach to those challenges.