Ship size and cruise length have the greatest impact on the number of ports you can visit, but the itinerary type and embarkation port also have an impact. Loop cruises begin and end at the same point and often visit ports in relatively close proximity to one another; one-way cruises start at one point and end at another, often exploring far-flung destinations. One-way cruises, which are more prevalent in European sailings than in the Caribbean, can often be combined for a longer voyage with no repeated ports along the way.

Typical one-week to twelve-night cruises include a day or two at sea, but ships on these itineraries spend as much time as possible docked in Baltic capitals and major cities. Departing from ports such as Copenhagen or Stockholm, highlights of Baltic itineraries may include Amsterdam, Oslo, Helsinki, Tallin (Estonia), and St. Petersburg (Russia); ships calling on St. Petersburg often dock for two or three nights there. Some itineraries may focus on a theme or specific region, such as cruises around the British Isles or Norwegian fjords and North Cape.

Some of the most popular Mediterranean itineraries, especially for first-time cruisers to Europe, are one-week sailings that embark in Barcelona and stop in southern European ports that range from Nice to Civitavecchia (Rome) and may include more exotic destinations like Malta and Corsica. A sea day might include a cruise through the narrow Strait of Messina or sailing past the volcanic island of Stromboli. Longer, one-way itineraries can even start in Lisbon and end as far away as Venice, while possibly calling at not only Gibraltar, the French Riviera, and Sicily, but Dubrovnik (Croatia) as well.

The most exotic and port-intensive cruises are those embarking in Venice, Athens, and Istanbul. Often one-way voyages, they are linked by the sea to coastal centers of antiquity such as Kusadasi (Ephesus) in Turkey and Katakolon (Olympia) in Greece, but also to Roman outposts of Dubrovnik and Korcula, Croatia. For a transit of Greece's historic Corinth Canal, you'll have to select an itinerary on one of the high-end Seabourn or SeaDream cruise lines' yacht-sized vessels. A sea day might be spent cruising past the grandeur of Mount Athos after leaving Istanbul or along the coastline in the Adriatic Sea. Best explored by small ship -- preferably one with sails that add to the allure -- Greek Island itineraries that include Santorini, Rhodes, and Mykonos are popular with honeymooners and couples for the romantic ambiance of sun-splashed beaches and leisurely al fresco meals accompanied by local wines and breathtaking sea views, but these ports are also visited by the larger ships, which must usually tender their passengers ashore.