Spectrum sensing is a critical prerequisite in envisioned applications of wireless cognitive radio (CR) networks, which promise to resolve the perceived bandwidth scarcity versus under-utilization dilemma. This talk presents recent advances for comprehensive situation awareness at the PHY of CR networks by capitalizing on the novel notion of spatio-temporal RF cartography, which amounts to constructing two families of maps: (m1) global power spectral density maps capturing the distribution of power across space, time, and frequency; and (m2) local channel gain maps providing the propagation medium per frequency from each node to any point in space and time. Paralleling the success of routing tables, the vision is to have CR nodes jointly utilize these maps so as to enable: (v1) identification of opportunistically available spectrum bands for re-use, and handoff operation; (v2) localization, transmit-power estimation, and tracking of primary user activities; and (v3) interference control, resource allocation, and routing. If time allows, CR sensing beyond the PHY will be presented too for flagging network anomalies.