As the app market expands, new challenges arise for developers. Creating useful applications is important in achieving extensive and cohesive use. This paper presents a mobile application called "The Time Machine", offering location-dependent information about the environment in a town. The app is evaluated through expert evaluation, as well as user evaluation conducted as a field observation with 15 participating users, measuring the level of usability in the application. Results are used to discuss guidelines on how to develop useful mobile applications. Knowledge about user behavior, a clear application purpose, an understandable interface, and cross-platform functionality are all important aspects for developers to consider.