The town lies at the foot of a rocky but tree-lined and naturally interesting clump, with the remains of a two-thousand-year-old fortress, militarily important already at the time of the barbarian invasions. Tunnels, moats, ruins from various eras and casemates testify to its strategic role through the centuries, from the disputes between the Serenissima and the Holy Roman Empire to the Napoleonic wars, the Renaissance and the wars of the 20th century It was not by chance that the Osoppo Brigade was named after the aggregation of secular, Catholic and socialist partisan formations immediately active in Friuli after Italy's armistice with the Allies on 8 September 1943.
Here, too, signs remain from the 1976 earthquake. In the reconstructed church of St Maria ad Nives, an altarpiece painted in the late 15th century by Pellegrino da San Daniele stands out.
On the opposite bank of the Tagliamento from Osoppo is Bordano, known for its' open-air gallery 'of almost three hundred wall paintings depicting butterflies and for three large greenhouses where hundreds of tropical butterflies flutter freely among visitors. An exhibition helps to understand the reasons for this only apparent strangeness, and to familiarise oneself with the unknown life of lepidopterans.