My daughter and husband are flying to Milan and will be in Lake Como for a wedding in September. They will have four days after that to explore somewhere else. I’m thinking Switzerland, but not sure exactly where and options to get there (via train). Then should they fly back out of Milan, or somewhere in Switzerland (Zurich)?
Ok, I'll be the first to suggest Lucerne here. Nice city, close to lots of things to see and do. Boat around lake Lucerne, Mt. Rigi, Mt. Stanserhorn, take a big loop through Lake Brienz and Lake Thun, visit Bern, etc... And a short train ride to the Zurich airport with lots of U.S. connections.
Lugano is less than an hour from Como city by train. Very nice lakeside location. Luzern is 2.5 hours by train. If they stay south, Lugano or even Locarno (more resort-like) flying out of Milan is best. If they go to Luzern, then Zurich for outbound.
Luzern, Locarno, and Lugano would all provide a nice taste without complicated transportation.
Where on lake Como will you be? That matters as its a big lake, and what part of Switzerland to visit is influenced by that.
You could go to Lugano, as suggested, but Ticino is very similar to the lake Como area, just cleaner, more efficient, but also more expensive. If you are on the east coast of the lake (eg. Varenna) you could go up to the Grisons via the Bernina railway, for something that is very different from the Italian lakes.