Cultural Heritage on Mobile Devices : Building Guidelines for UNESCO World Heritage Sites Apps Technological improvements and access provide a fertile scenario for creating and developing mobile applications (apps). This scenario results in a myriad of Apps providing information regarding touristic destinations including those with a cultural profile such as those dedicated to UNESCO World Heritage Sites (WHS). However not all of the Apps have the same efficiency. In order to have a successful app its development must consider usability aspects and features aligned with reliable content. Despite the guidelines for mobile usability being broadly available they are generic and none of them concentrates specifically into cultural heritage places especially on those placed in an open air scenario. This research aims to fulfil this literature gap and discusses how to adequate and develop specific guidelines for a better outdoor WHS experience. It uses an empirical approach applied to an open air WHS city: Weimar and its Bauhaus and Classical Weimar sites. In order to build a new set of guidelines applied for open air WHS this research used a systematic approach to compare literature based guidelines to industry based ones (based on affordances) extracted from the available Apps dedicated to WHS set in Germany. The instructions compiled from both sources have been comparatively tested by using two built prototypes from the distinctive guidelines creating a set of recommendations collecting the best approach from both sources plus suggesting new ones the evaluation.