With crisp air, cool temperatures and brilliant foliage on display, autumn is an ideal time to cruise. The stretch between summer and winter affords relatively crowd-free ports and fewer passengers on board (kids are back in school), translating to plenty of opportunities to commune with nature. Best of all, many repositioning cruises — ships crossing from one region of the world to another — offer reduced rates and longer itineraries.So, if you're one of the nearly 21.7 million passengers projected to cruise in 2014, fall is an ideal time to take in striking backdrops and score significant savings. Decide which sailing is right for you with U.S News' list of the top autumn cruise destinations and itineraries.Note: All prices were correct as of Aug. 20, 2014 and are per person, based on double occupancy.In Pictures: Best Places to Cruise This Fall Alaska is known for its jaw-dropping scenery: Calving glaciers, snow-capped peaks and majestic fjords snake along quaint towns and villages. And in September, the waters teem with humpback whales and sea lions. Many large ships, such as those within the Princess Cruises and Celebrity Cruises fleets, offer travelers the chance to explore the Inside Passage with stops in Juneau, Ketchikan, Sitka and Victoria, British Columbia. Smaller cruise ships, such as those operated by Un-Cruise Adventures, also navigate the Inside Passage of Southeast Alaska, with home ports in Ketchikan, Juneau and Sitka. Many cruise lines also offer voyages to the narrower Gulf of Alaska passage, taking passengers from Vancouver and to Anchorage (or vice versa), making stops in hard-to-reach ports like College Fjord and Hubbard Glacier. Though both routes offer ample nature-viewing opportunities, the latter tends to lure those in pursuit of more immersive offshore experiences and face-to-face wildlife encounters.An eight-day trip aboard Un-Cruise Adventures' Wilderness Discoverer departing from Sitka on Sept. 13 is listed at $1,895 for a Navigator cabin. That's $700 less than the price advertised for the same cruise (and cabin category) leaving on May 23, 2015. Entry fees to national parks, onboard meals and equipment (like hiking poles and paddle boards) are included in the rate. The price also covers three days in Glacier Bay and expeditions through southeast Alaska's Icy Strait, not to mention an abundance of wildlife viewing.Princess Cruises lists a seven-day cruise in an ocean view room on Golden Princess from Seattle to Juneau on Sept. 6 for $968 per person. For the same cruise departing on Aug. 22, 2015, you would pay an additional $500. The main draw of this trip is Glacier Bay National Park, where park rangers climb aboard the ship to offer their knowledge of the landscape and direct you to popular wildlife viewing spots. And if you're looking to tack on extra days before or after your journey, Princess Cruises offers "cruisetour" packages that can include stays at Princess-affiliated wilderness lodges and land-based activities, such as glacier-flightseeing and whale-watching.See: Best Luxury Cruise LinesEvery fall, vibrant autumnal hues color coastal cities across New England and Canada. And a number of cruise companies offer trips to foliage-rich locales like Portland and Bar Harbor, Maine, Québec City and Montreal. Apart from scenic drives in seaport towns, many large and small ships, including those within the Holland America, Celebrity Cruises and Crystal Cruises fleets, also provide the chance to sample local New England cuisine (think fresh Bar Harbor lobster). To help pinpoint the best coastal cruise for you, peruse itineraries that deliver a high off-season value and ample opportunities for fall leaf peeping.Holland America lists a seven-day cruise aboard the ms Maasdam leaving from Montreal on Sept. 20 with calls in Québec City and Bar Harbor, Maine. An ocean view room is advertised at $799 per person, which is $200 less than the same cruise leaving on May 16, 2015. During days at sea, you can slip away to Greenhouse Spa & Salon for a hot stone massage or sign up for cooking classes at the Culinary Arts Center. Though Holland America offers fewer shore excursions compared to other cruise lines, days at port can include anything from navigating Prince Edward Island National Park to exploring Cadillac Mountain.Crystal Cruises' Crystal Serenity departs on Oct. 11 from Halifax, Nova Scotia, to New York City for a five-day journey, with fares for a deluxe stateroom listed at $1,780 per person. If you book your room by Aug. 29, your cruise rate will cover Champagne, wines, spirits and all other beverage costs. Plus, the price of your cruise will include enrichment classes, such as digital film-making and dance lessons, and a complimentary meal at one of the ship's specialty restaurants.See: Land vs. Sea? A Cruise May Be More Affordable Than You Think Caribbean-bound cruises offer significant deals during the fall sailing season. But there's one caveat: Your trip runs the risk of being impacted by weather-related interruptions until hurricane season ends in late November. To protect yourself against unforeseen weather delays, purchase travel insurance and confirm that your insurance provider covers trip interruptions. Should you decide to take your chances, last-minute sales — especially for journeys departing in October and November — are aplenty. Behemoth lines like Royal Caribbean International and Disney Cruise Line operate in the Caribbean year-round, often affording excellent savings in the off-season. Shorter four- or five-day sailings aboard these lines can also yield steep discounts.Royal Caribbean's Oasis of the Seas departs from Fort Lauderdale, Florida, on Oct. 27 for a five-day cruise to the Western Caribbean, with stops in the Bahamas and Cozumel. The price for a balcony room is listed at $554 per person. Shore excursions include tours of the Mayan Ruins in Cozumel and snorkeling along reefs in Nassau. During your sail, you can take your pick of 10 pools, Tai Chi classes or treatments at the Vitality Spa, among other activities.Disney Cruise Line's Disney Wonder leaves from Miami on Oct. 17 for a five-night cruise to the Western Caribbean with stops in Grand Cayman and Cozumel. The fare for an ocean view stateroom is listed at $1,383 (including all fees and taxes) per person. At sea, you can enjoy sea wrap treatments at the Vista Salon & Spa by day and Broadway-style performances and cocktails at the piano bar after dusk.See: Best Cruise Lines for the MoneyIn the off-season, many ships depart from one part of the world and finish in another in what's known as "repositioning" sailings. These trips, which typically take place in the spring or the fall, often provide deep discounts and more days at sea than regional cruises. Popular journeys include transatlantic crossings from Europe, sailings across the Pacific from Hawaii to California, Caribbean-bound voyages from California and departures from the Caribbean to the Panama Canal. Many megaship and smaller cruise ship lines — including Norwegian, Celebrity and Oceania Cruises — offer fall repositioning cruises with varying departure and disembarkation ports that fit a wide range of budgets.Celebrity Cruises' newest ship, the 3,046-passenger Celebrity Reflection, leaves from Rome on Oct. 17 for a 15-night cruise to Miami, with calls in Madeira, Portugal, St. Kitts and St. Maarten, among other ports. An ocean view room is priced at $1,249 per person (excluding taxes, fees and other port costs). While at sea, you can retreat to the Alcoves, an exclusive area for cabana lounging and picnicking, dine at six specialty dining venues and partake in cooking classes at the Art Studio, a space tucked inside the ship's top-deck Lawn Club.Oceania's Riviera departs from Barcelona on Nov. 15 for a 14-day voyage to Miami. Thanks to a two-for-one early booking promotion until Sept. 3, 2014, which includes half-priced deposits and flight upgrades, you can book a deluxe ocean view stateroom for $3,799 per person. That’s roughly $7,300 less than the advertised brochure fare. Highlighted trip excursions include exploring the Alhambra in Granada and navigating Blue Lagoon Island from Nassau. Back on the ship, you can retreat to one of six gourmet dining venues or sign up for an interactive cooking lesson at the Bon Appétit Culinary Center.In Pictures: Best Places to Cruise This FallLiz Weiss is an editor for the Travel section at U.S. News. 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