Monte Orsa, Mountain summit in Viggiù, Italy.

Monte Orsa is a mountain in the Varese Prealps near Viggiù, rising to about 1000 meters with views toward Lake Lugano. Several marked trails connect different starting points across the area, linking the nearby towns of Saltrio and Viggiù.

During World War I, the mountain formed part of the Cadorna Line defense system, a major fortification across northern Italy. Trenches, tunnels, and observation posts built during that period remain visible on the slopes today.

The mountain's karst system draws speleologists to caves such as Mamma Emma and the Pozzo del Caprone. Above Viggiù, the north-west facing crag near the summit is equipped for sport climbing, and a small bouldering area has been mapped on the slopes above Besano.

Since 2013 the asphalt road from Viggiù to the summit has been reclassified as an agro-silvo-pastoral track, so it can no longer be driven. Access is on foot; the equipped crag near the top faces north-west and is used for sport climbing in summer. The karst system, with the Mamma Emma cave and the Pozzo del Caprone, is visited by cavers.

Two large signal repeater antennas stand at the peak, visible from far away and marking the skyline. These modern installations contrast with the historic trenches and tunnels preserved lower on the slopes.