The central element around which much of the activity of a team of researchers, technologists, and technicians from INGV has been developing for years is extending and integrating the monitoring networks developed on land with observation points at sea in strategic sites. Having observation points at sea allows us not only to analyze geophysical phenomena from a different perspective but also to increase our understanding of the complex processes of land-ocean-atmosphere interaction. Thanks to the acquisition of long time-series of data, underwater observatories play a fundamental role in monitoring a wide range of natural processes, from the occasional short-time scale ones (such as earthquakes and tsunamis) to those that exhibit long-term variability period (for example the warming of the seas).