In January 1910, a chalk mine at Château-Landon in the Paris basin brutally collapsed, causing 7 fatalities. This dramatic event was related to the centennial flood of the Seine River and one of its tributaries, the Loing River, which invaded the lower parts of the mine and eventually weakened the entire structure. To understand the conditions that triggered the disaster and anticipate other catastrophic event of this kind elsewhere, the Royer mine, located in the same area, was chosen to host an underground scientific observatory. Its goal is to study water–rock interactions and in particular water circulation and unusual ground saturation conditions on the behaviour of chalk. The Royer chalk mine is shallow, above the water-table, easily accessible and globally stable. It has been equipped with a high resolution multiparameter monitoring network in 2019; all the sensors are connected to The French National Monitoring Centre for Ground and Underground risks (Cenaris). Besides from in situ observations and monitoring, series of laboratory tests are carried out on samples to study the impact of hydraulic cycles on the short- and long-term behaviours of chalk. A hydromechanical model is also under development to analyse the results and better assess the overall stability of the mine in the context of climate of change. In this paper, we provide a brief summary on the challenges to assess geohazards from abandoned chalk mines, and then present in detail the observatory, its objectives and perspectives, as well as the first results after two years of activity.