Day trip from Varenna

Drive to St Moritz over the Maloja Pass. Or stop short at Sils Maria and take the cable lift up to Furtschellas.

OR, take the ferry to Menaggio and the bus into Lugano. We enjoyed a lovely lunch on the lake.
Then, we rode the train into Como for dinner and took the ferry back into Varenna.

Thanks for the suggestions!

Drive to Tirano (or better, Poschiavo). Ride the train up to Alp Grum and have lunch. All that's up there is a station, restaurant and small B&B, all in the same stone building. You'll have lunch on the terrace of the restaurant with a great view of the Palu glacier over one shoulder and Italy over the other. The only thing you'll hear besides the other diners is the occasional train whistle, birds and perhaps cows mooing. Google it - you'll see what I'm talking about.