Staying 3 nights...ideas as what to do and see?

Not really much to go on here - what are your interests, do you have a car or are you reliant on public transport, Where on the lake are you staying?

It's been some years since I was last there, but Monte Isola (possibly the biggest lake island in Europe) was pleasant. I particularly enjoyed getting a one day ferry pass and just spent the time jumping on and off the ferries anywhere that took our fancy.
If you have transport, Bergamo is worth a day trip, there are also some very scenic drives around that area.

Thanks so much for your quick reply Planning on going to Monte Isola and yes we have transportation, so thats not a problem. And, we will look at Bergamo.
Staying at Araba Fenice

If you are interested in prehistoric rock carvings, Capo di Ponte is a must (direct trains from Iseo).
You may also go by train to Edolo, by bus to Tirano and bord there the Trenino Rosso (BERNINA).
Or visist the historic city center of Bergamo,.

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