I'm assuming you've read this on NCL's website?
"Schengen States: Austria, Belgium, Denmark, Finland, France, Germany, Greece, Iceland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, and Sweden. The Schengen Agreement came into force on 26 March 1995. It is an agreement between several member states of the European Union (EU), to remove immigration controls for travel within their collective territories. This creates a “borderless” region, known as the “Schengen Area” and therefore changes the procedures for entering or connecting in all of the Schengen States as well as for traveling between them. There are four types of Schengen visas, but type C is the one typically needed by passengers, which can be issued by any one of the Schengen states and is valid for all the others. Due to the type of itineraries in Europe, Scandinavia, and the Mediterranean, passengers that do require Schengen visas must obtain a multiple-entry type visa prior to traveling. U.S. and Canadian citizens do not require Schengen visas."
I "Googled" Schengen visa and found this site that might be helpful. There are quite a few sites listed besides this one:
Hope this will help you,