We have settled on Locarno as our first stop for our tour of Switzerland. We are flying into Linate and wanted to start in one of the lake towns or villages thrt was convenient to transfer to the Swiss train network; the candidates that seemed to work best for that were Milan, Varenna (or another town along the east side of Lake Como), Lugano or Locarno. We looked briefly at Como but liked the more scenic towns in the list above. Locarno has the benefit of being the starting point for the Treno Gottardo, the scenic train that follows the original train route across the Gotthard Pass to Lucerne (our second stop), so it moved to the top of the list.
What I have come up with so far is this list of activities: funicular to the Madonna del Sasso monastery and the cable car to Cardada with a possible hike at the terminus (suggestion from Ken-thanks!), a cruise on Lake Maggiore, a stroll through the old town, a visit to Castello Visconteo and a day trip to the castles in Bellinzona. If we feel really adventurous, we might check out paragliding over Lake Maggiore or a bungee jump from the "Golden Eye" dam, but after a long flight from the US, I think we will likely spend our sightseeing time on the ground.
Anyway, that seems like a pretty complete list and certainly justifies spending several days in Locarno. If anyone her has any other suggestions for sights or activities, I would welcome the input. Thanks!