Ravella is a stream from the southern side of the Corni di Canzo, at about 1,000 m altitude, on the lower edge of Colma dei Corni, where glacial clay crops out from under a mantle of alluvial sediment. It flows down into the Old Town of Canzo. Its basin, lengthened in an east-west direction, is bounded by Cranno's crest, Colletta, Corni, Colma dei Corni (north), and by Maschèrpa and Mt. Prasanto (east). To the south, the basin of Ravella includes parts of Mount Raj, Mount Cornizzolo and Pesora. Its affluents are the small rivers of St. Mir and of Valett, the last flowing down from Pesora and entering Ravella not far from St. Francis' church, passing between the convent's lands and the "curt di Sant", flowing under an ancient bridge and entering Ravella between the former Prina and Arcellazzi palaces. The River Ravella, in its upper course, often flows through steep limestone canyons, resulting in small waterfalls and with characteristic "giants' mufflers", produced by the action of glaciers, parallel to the anticline and syncline folds forming the structure of the Lombard pre-Alps.