Under illumination, metal nanoparticles can turn into ideal nanosources of heat due to enhanced light absorption at the plasmonic resonance wavelength. In this article, we aim at providing a comprehensive description of the generation of micro-bubbles in a liquid occurring around plasmonic nanoparticles under continuous illumination. We focus on a common situation where the nanoparticles are located on a solid substrate and immersed in water. Experimentally, we evidenced a series of singular phenomena: (i) the bubble life-time after heating can reach several minutes, (ii) the bubbles are not made of water steam but of air and (iii) the local temperature required to trigger bubble generation is much larger than 100°C: This last observation evidences that superheated liquid water, up to 220°C, is easy to achieve in plasmonics, under ambient pressure conditions and even over arbitrary large areas. This could lead to new chemical synthesis approaches in solvothermal chemistry.