The digital traces that people continuously leave behind – voluntarily or not – while using communication devices such as mobile phones or interacting with social media platforms reflect their behaviour in great detail. In this paper we show examples of the spatio-temporal patterns of collective human dynamics, which we derived from ‘social sensor’ data. We used user-generated data in mobile networks and voluntarily published information at social media platforms, which both served as proxies for human activity and mobility. Results show collective human activity and mobility hotspots in selected European urban environments and thus provide additional insights into how collective social activity shape urban systems. We used different geo-visualisation techniques to effectively communicate the urban inherent spatial and temporal dynamics. Especially for education related purposes, this allows a better general understanding of collective human behaviour in urban environments.