The Visitor Centre Gradina is located on the slope of Colle Nero/Črni hrib, on the site of a former stone quarry. With its environmental and historical museum, the centre is a reference point for the Natural Reserve of the Doberdò and Pietrarossa lakes (Riserva naturale dei laghi di Doberdò e Pietrarossa). The protected area involves three municipalities: Doberdò del Lago/Doberdob, Monfalcone/Tržič and Ronchi dei Legionari/Ronke. The reserve is characteristic for its two large karst depressions, each with an intermittent lake. A limestone ridge separates the water surfaces of the two lakes.