See amazing glaciers within Glacier Bay National Park.
See amazing glaciers within Glacier Bay National Park. Michael Melford/Getty Images

Every Alaska cruise itinerary brings such delights as soaring eagles and massive glaciers, but you'll get even more from your cruise if you understand the geography.

America's 49th state is basically divided into two separate and distinct cruising areas, the Inside Passage and the Gulf of Alaska.

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Here's what you need to know about each:

Inside Passage

On this, the most popular Alaska cruise itinerary, your ship explores southeast Alaska, specifically the narrow strip that runs from the Canadian border in the south to the start of the gulf in the north (locals call it the Panhandle). Southeast Alaska includes Juneau, the capital city; the fishing town of Ketchikan, known for its Native Alaskan totem poles; and the gold rush town of Skagway. The Russian-influenced town of Sitka is also a port of call on some itineraries.

On these seven-night cruises, views include rainforests (yes, rainforests), mountains and inlets — all areas rich in wildlife. You also view amazing glaciers such as Margerie, Johns Hopkins, Muir or others within Glacier Bay National Park, with a chance to experience the awesome sight and sound of glacial calving (the sudden breakaway of large ice chunks). An advantage of this Alaska cruise itinerary, as offered by companies like Norwegian Cruise Line, is that you can do it round-trip from either Seattle or Vancouver.

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Gulf of Alaska

On a weeklong Gulf or Glaciers Alaska cruise itinerary, you explore south-central Alaska. These cruises are between either Seward or Whittier (both near Anchorage) and Vancouver. This route doesn't mean you don't visit any of the Inside Passage — you typically call at the same ports, seeing many of the same sights. The big difference is that these cruises are one-way — either northbound or southbound.

The scenery here is dazzling — College Fjord, for instance, is lined with 16 glaciers. Spending a few days pre- or post-cruise in Anchorage or the nearby Kenai Peninsula and Denali National Park is highly recommended (cruise-tour packages are available from the cruise lines).

Other options

While big ships with thousands of passengers pamper you with every resort amenity imaginable, they tend to visit tried-and-true ports — with shore excursions that include whale-watching excursions and once-in-a-lifetime thrills such as dogsledding on top of a glacier.

A small, casual ship that's following a different kind of Alaska cruise itinerary, meanwhile, typically spends more time in the wild. An example: InnerSea Discoveries has a weeklong itinerary from Juneau on its 86-passenger Safari Endeavour that visits Glacier Bay National Park for two days and other wilderness areas in search of wildlife, including whales. On these cruises you spend more time in kayaks or skiffs than on land.