Just about an hour easy drive from Stresa, the Parco Naturale dell'Alta Valle Antrona offers many walks, from easy to difficult, from 40-minute strolls around tiny lakes, to day journeys for serious trekking. There are 18 natural lakes here, and six man-made lakes.
At Lago Camplicciolo walk along the tracks of an old mining train and through mining tunnels
At around 1,400 meters altitude
That particular color of some Alpine lakes - Lago Camplicciolo
Walk under a waterfall at Lago Antrona
Just as an example, here's what we did: We drove to Lago Camplicciolo (an artificial lake created by one of the hydroelectric dams), parked the car there, and we walked the 1.5 hour giro del lago (loop around the lake). Once back at the car we drove back down to Lago Antrona, had a relaxed lunch at Ristorante Bar Lago Pineta, and after a hearty lunch walked from there around Lago Antrona (there are charming picnic areas distributed all around the lake as well). This second lake loop took only 45 minutes.
Take a look at these websites for tons of information: http://www.valleantrona.com/ and http://www.parcovalleantrona.it/Eindex.php