This paper advocates a visitor-centric approach to designing a solution for navigation and interpretation.  The American Museum of Natural History iPhone application Explorer combines state of the art location awareness, interpretation, and social networking to deliver an enhanced visitor experience both onsite and online.  AMNH had three objectives with this project: to facilitate visitor navigation, to provide an application that appeals to visitors and encourages repeat visits, and to enhance exhibit information without detracting from the exhibits themselves.  This paper examines the reasoning behind utilizing a mobile device for wayfinding; the choice of the iPhone platform; the challenge of bringing "GPS indoors" and the resultant technical solution; feature set determination and usability; the role of mobile devices in the pre- and post-Museum visit continuum; the challenges of curated mobile content creation; deploying the application on Museum-supplied devices and through the iTunes store;  and marketing of the device and app.  The authors present the challenges faced by AMNH in executing a cross-Museum enterprise and share lessons learned, in order to offer the wider museum community an opportunity to build on our experience and expertise.