Rome > Naples > ???

Planning an adventure holiday to see as much of Italy in 7 days 23rd > 30th August.

We have decided to fly to Rome > stay a few nights > train to Naples, stay 1/2 nights > travel on down south > fly back out of Naples on 30th Aug.

Any suggestions for the third location? Sorrento looks appealing.

Ideally we want to be hiking / renting bikes / walking and seeing sights.