The Sani Environmental Observatory (S.E.O.) is located within a mature, near-coastal Aleppo pine (Pinus halepensis L.) ecosystem at the peninsula of Kassandra, in Chalkidiki, Greece. It is part of the Stavronikita forest, which comprises approximately 300 ha of land covered mainly by forests and to a lesser extend by shrubs and pastures. The Observatory aims primarily at the assessment of the carbon and water balance of this typical low-elevation forest ecosystem to the ongoing climatic shift. Such ecosystems may be prone to the intensified heat and drought events, as well as to the associated insects’ and pathogens’ outbreaks, which are increasingly occurring at the Mediterranean region and particularly at its eastern part. Although Aleppo pines, as well as other Mediterranean pines, are generally adapted to the region’s xerothermic conditions, the in-depth understanding of their ecophysiological and growth responses will allow us to predict the potential of such ecosystems to adapt to climate change. SEO also serves to assess the carbon stocks and fluxes and the contribution of these natural, old-growth ecosystems to carbon sequestration and, thus, to climate change mitigation. S.E.O. is developed by the Forest Research Institute (Lab of Forest Ecophysiology) of the Hellenic Agricultural Organization Dimitra with the support of Sani Resort SA, the owner of the studied forest ecosystem, presenting a nice example of collaboration between the research community and the private sector. Given that SEO is located at a region of high touristic and aesthetic value, close to a wetland and the sea, the Observatory also plans actions to familiarize people with environmental monitoring and the multiple functions and services of the studied Mediterranean ecosystem.