Venice

By train, stop at Stresa on Lake Maggiore. Right on the rail line.

Are you travelling by train or car (you mention car in your other post)?

Suggestions: Lake Garda, One of the towns on the North Italian Plain, e.g. Verona, somewhere on Lake Como, Stresa on Lago Maggiore, Lugano, Belinzona (3 castles!).

BTW, the spelling is "Interlaken".

This is a popular question today. See also:

https://community.ricksteves.com/travel-forum/switzerland/switzerland-to-venice

https://community.ricksteves.com/travel-forum/switzerland/which-rail-pass-and-how-to-get-to-venice

You can get from Interlaken Ost to Venezia S. Lucia station in as little as 6.5 hours with two connections. If departing Muerren, travel times to Venice vary from 7.5 to 10 hours; the faster timings may require more connections.

Lugano would be a logical overnight stop along the route of the faster trains and close to the edge of coverage for a Swiss Travel Pass. Then you'd buy a regular ticket for the next day's travel, mostly within Italy.