In recent years, we witnessed: the progressive instrumentation of our cities with diverse sensors; a wide adoption of smart phones and social networks that enable citizen-centric data acquisition; and a growing open release of datasets describing urban environments. As a result, nowadays it is becoming possible to make sense of all those data sources using semantic technologies together with streaming data analysis techniques. In particular, being able to feel the pulse of the city can allow delivering new services for the large number of organised and spontaneous events that take place in our cities. This talk frames the problem space, presents the challenges, proposes a solution centred on RDF stream processing that was applied to several case studies, and discusses the open problems that may be of interest of the Semantic Web community.