Our tour of Borromeo Palace on Isola Bella was arranged by the tour group we were a part of. We were inside the Palace a total of 15 to 20 minutes, I have never been on such a rushed tour, it was so disappointing. I would have like to have been able to spend some time looking around and taking in the different rooms. Our guide was very entertaining but his intend was to move us along and that he did. We never saw the grotto's and I realized after buying a book on the isle in the book store. Then I realized how much we missed of the Palace, disappointing.
I would not miss Isola Bella if you traveled to the area. The gardens are amazing, I would try to see if you could get a longer tour which showed more of the Palace.