There are so many places to see in Europe that you couls spend a lifetime touring in the Old Continent.
Paris and Rome are great places to start. Both of those cities have a lot to see.
Carnival Liberty New Year's Eve 2007
Liberty of the Seas 5/2008+11/2009
Allure 1/16/ 2011
Independence of the Seas 12/29/2013 Top-notch!