The Valle Olona is a valley stretching from just south of Bregazzana, a hamlet of Varese, to Castellanza in northern Italy.
Carved by the Olona River, from which it takes its name, the valley formed during the Riss glaciation due to the erosive action of a glacier descending from Lake Lugano. Over subsequent centuries, the Olona River partially filled the valley's alluvial zones with gravel and sand, and later, through repeated flooding, deposited substantial sediment that now supports diverse plant life.
The Valle Olona typically features a valley floor devoid of settlements, except for Castegnate (one of two hamlets of Castellanza, located at the valley's outlet) and the hamlets of Gornate Olona, namely Torba and San Pancrazio. Farther north, one of the last inhabited areas is the Mulini di Gurone, which also hosts a dam designed to protect downstream settlements from Olona River floods.
Scattered across the valley floor and nestled among numerous wetlands and broadleaf tree forests that cloak the surrounding slopes are remnants of abandoned industrial complexes and several water mills along the Olona, once vital to local economies.
The valley also encompasses the route of the Valmorea railway, once abandoned but now repurposed as a cycling and pedestrian path between Castellanza and Castiglione Olona. Part of the line was refurbished to accommodate a tourist train between Malnate and Mendrisio until 2013. Plans are underway for the Ciclovia Olona Lura, a 165 km loop connecting the valley to the Lura stream along the European EuroVelo 5 route.
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