ClustTour, a city browsing and photo tagging mobile app, won the demo award at this year's International Conference on Multimedia Retrieval (ICMR 2012) in Hong Kong. The app, which is available for free on the app store, supports efficient browsing and tagging of landmark and event photos. The application employs a hierarchical mode of exploration enabling zooming from the level of a city, through the level of an area/neighbourhood, down to the level of a specific spot. This navigation mechanism combined with photo clustering, and a dual map-list viewing mechanism, makes possible the browsing of hundreds of thousands of publicly available geotagged photos on a smartphone. To reduce clutter on the screen caused by the large number of markers on the map, an adaptive clustering strategy is employed. In addition to the advanced browsing capabilities, the application enables users to import their personal photos from Flickr and to easily annotate them by propagating to them metadata (location, tags) from the currently viewed object (area, landmark). The application currently supports more than 30 cities worldwide.