Hi there, suggestions for a few of your stops ....
Istanbul - a visit to the Grand Bazaar is a must with over 60 covered streets and 3000 stalls. Not for those who don't like crowds though.
Naples - although the obvious tour is to Pompeii, take a look at Ercolano (aka Herculaneum). It is smaller, but for more complete, and was so quickly covered that much of it looks brand new - but it is all original
Florence (Livorno?) - it is a very long day, but if you are only visiting the once, you really need to take an organised trip to Florence & Pisa.
Barcelona - There are good hop-on hop-off buses in the city, but plan ahead as some routes take up to 3 hours.
Alternatively take a trip to Gaudi's Guell park, for a close-up of some of his bizarre buildings. If you search the photos here, we have previously posted a selection there.
Tenerife - for something really different, take a look at the Loro Park site, the Park has shows, Sealife, Birds, Wild animals, aquariums, arctic animals & so on. It is a full day's entertainment.
Hope those give you some ideas,
Have a great cruise,
Last: Cunard Queen Victoria January 2016
Next: Oceania Marina June 2016
Then: P&O Oriana August 2016
Then: P&O Oceana December 2016
Golden, Grand(2), Caribbean, Royal, Sea(4+1 aborted)
Adonia(4+2), Arcadia, Artemis(2), Aurora(5), Azura(2), Britannia, Oceana(3), Oriana(12), Ventura(2), Victoria(5)
QM2(2), QE2(9), QV(7), QE, Caronia(2), Minerva, Minerva II, Fred.Olsen(8), NCL Jade, =X= Eclipse, HAL Ryndam, Aza.Journey