This valley has got many foot paths from the easiest to the hardest.
Stops you must do are: the church of Mogno (Fusio), The little village of Bosco Gurin, The waterfall of Foroglio. www.vallemaggia.ch
From San Carlo you can take the cable car to Robiei (1900 meters). www.robiei.ch
Most important is the Dam which is one of the most highest in Europe (220 meters), where you can also do some bungee jumping. Another stop is at the famous bridge of the 2 arches.
This valley goes from Locarno to Domodossola it is a most charming trip which you can take by car or by train. www.centovalli.ch