Onsernone Valley is lying from Centovalli Valley as far as thermal springs from Graveggia in Italy. At the bottom of the Valley, Isorno River is shaped by narrow and deep gorges from the rough and wild character of Onsernone Valley. Just before, the two rivers (Isorno and Melezza) meet together and flow into Centovalli Valley, which opens the Valley as far as a large bend by a big cleft among the mountain sides covered with thick forests of chestnut trees.

There are some big sunny platforms in Onsernone Valley which were formed in the Ice Age are nowadays occupied by a lot of picturesque villages.

The region around "Lago Maggiore" is the sunniest in Switzerland with 2300 hours of sunshine in the year!