The sulfatara geosite of Monterano, included in the list of sites of the geological heritage of Lazio, is a vast mineralised area along the Mignone River, at the foot of the tuff cliff of Monterano. These are thermo-mineralised waters with strong emissions of gas vapours in the vicinity of old mines for the production of pyrite, iron and marcassite. The flow rate of the spring gushes varies between 0.5 and 2 l/sec, with a temperature of about 22° C. The presence of sulphate salts prevents the development of vegetation near the springing points: in the surroundings, we find instead the presence of Poa Annua, Agrostis Canina and Paspalum Distichum, as well as some types of lichens. It is worth pointing out as a source of pride the presence of a beetle, the Cicindela – normally found along sandy coasts – which is instead found exceptionally in this site as well as in the caldara of Manziana. The esplanade scattered with springs of sulphurous bubbling water is reached after an itinerary that starts from the Diosilla Waterfall, a splendid natural spot with characterised by particularly unusual colour shades, ranging from rust yellow to blue and whitish. After leaving the waterfall, we pass through tuff walls and natural rock arches immersed in a forest of oaks and rare ferns.