Themed cruise-ship expeditions of all kinds are nothing new. It’s easy to find one featuring something that floats your boat, whether you’re into opera, wine, pirates, or military history. But that’s just the beginning. It turns out that mankind is even more obsessive than you (or we) could have ever imagined.

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Edvard Grieg Cruise
Fans of “In the Hall of the Mountain King” and Peer Gynt can sigh with relief: Their cruise needs have been met, thanks to the folks at Blue Water Holidays. This eight-night voyage, titled “The Life, Work, and Music of Edvard Grieg,” promises a cornucopia of details about the man’s life and his impact on Norwegian music. Starting from the southern city of Bergen, this Grieg-athon hops from fjord to fjord up the coast of Norway, passing into the Arctic Circle and continuing on to the Russian border. Concerts, piano recitals, and lectures mingle with a visit to Grieg’s home at Troldhaugen and endless views of Norway’s dramatic scenery. Die-hard Grieg-ophiles can even extend the trip to 12 nights if they feel so compelled.

Caribbean Knitting Cruise
One of the world’s most popular cruise destinations is the Caribbean, with its royal blue waters and sun-drenched skies. What could possibly improve such a tranquil journey? Celebrity knitting, of course. Great Balls of Yarn, which bills itself as South Florida’s “gourmet knitting store,” has put together a trek devoted to all things knitting. The Norwegian Sun departs from Miami, and its stops include Mexico, Belize, and the private Bahamian island of Great Stirrup Cay. Aboard is special guest Lily Chin -- celebrity knitter, author, and designer -- who is perhaps best known for crocheting an entire sweater for David Letterman in 40 minutes during an appearance on his show. The trip includes eight days and seven nights of sun, fun, and knitting seminars.

Container-Ship Cruise
For travelers seeking a more bare-bones cruise vacation, the folks at Freighter World Cruises regularly book trips aboard cargo vessels. These voyages can span from two weeks to four months in duration, and when the tour operators say “informal and casual surroundings,” they’re not kidding. There are no crowds, no dressy parties, no clocks, no Internet, no elevators, and no activities of any kind other than regular meals with the ship’s crew. You’ll spend quiet days (and days and days) at sea, and your only companions will be a dozen other passengers, a European and Filipino crew, and thousands of containers of cargo carrying everything from fruit to heavy machinery to household goods to hazardous materials.

Simple Man Cruise
The Southern rock band Lynyrd Skynyrd takes fans and friends on a four-day Simple Man Cruise from Miami to Key West to Calica, Mexico. On board are several similar country-fried bands, such as the Marshall Tucker Band, the Georgia Satellites, Backyard Tire Fire, Cowboy Mouth, Blackberry Smoke, and the Zac Brown Band. The voyage features plenty of live music, an open-mike night, and multiple opportunities to wave your lighter in the air. Cruise producer Sixthman also packages other themed sails, which feature acts like John Mayer, Lyle Lovett, and Barenaked Ladies, but the Simple Man Cruise (named for a classic Skynyrd song) promises to be the only trip during which you can swig from a longneck Bud and holler “Free Bird” without there being irony.

Goth Cruise
Each year, the Caribbean is blessed with the arrival of a cruise ship filled with pale-skinned people wearing black clothing. The annual Gothic Cruise and Masquerade Ball has been touring since 1989, escorting passengers in top hats and gowns from Florida through the Virgin Islands and on to Nassau. Highlights of the trip include live concerts, a gothic fashion show, a masquerade ball, and formal dress-up dining. However, there are some restrictions: Hooped gowns should be less than three feet in diameter in order for the wearer to be able to navigate the dining room, and spiked collars are okay, but spiked armbands are not permitted because they can ruin the plush seating.

Super Elite Cruise
One downside indigenous to most travel is that you can’t completely avoid the riffraff. The Four Seasons aims to eliminate that problem entirely by launching its Four Seasons Ocean Residences in 2010. Essentially, passengers will book their own fully furnished superluxury apartment aboard a 12-deck private ship and then circle the globe, touring the world’s greatest cities without bumping into anyone beneath their tax bracket. The maiden voyage departs from Helsinki and continues for two years. Cabins — er, residences — vary in size from one- to four-bedroom suites and may be up to 7,800 square feet. A crew of 220 provides concierge service, and onboard amenities include four restaurants, an art gallery, boutiques, a wine cellar, a meditation garden, a gourmet market, and a helipad.

Chocolate Cruise
Chocoholics converge for this seven-night cacao binge aboard the 700-guest Seven Seas Voyager, which departs from Florida and explores select islands in the Caribbean. As one would hope with 700 chocolate fiends aboard, the emphasis here is all about the chocolate — there are chocolate chef ’s tastings and demonstrations, chocolate desserts, a chocolate tea time, chocolate trivia, chocolate lectures, and discussions about the history of chocolate. Four dining venues, including one operated by Le Cordon Bleu, crank out signature chocolate desserts and other specialties. And for the totally uncontrollable chocolate addict, shipboard gratuities include 24-hour room service.

Neil Diamond Tribute Cruise
Couples in Seattle looking for a special romantic evening on Valentine’s Day need only one man: Neil Diamond. Each year, Argosy Cruises organizes a Neil Diamond Tribute Cruise and Valentine’s Dinner, during which passengers can whisper sweet nothings to each other while being accompanied by the passionate love songs of the Diamond. The Northwest’s premier Neil Diamond tribute band, Cherry Cherry, serenades the guests with renditions of, well, “Cherry, Cherry,” “Sweet Caroline,” and “Kentucky Woman.” Argosy provides a special four-course dinner, which includes a Champagne greeting and fountain soda. An added bonus for lovebirds: Couples have their very own table, rather than share one with other cruisegoers.

Homer’s Odyssey Cruise
It’s been nearly 3,000 years since Homer wrote his epic about Odysseus making the journey home after the fall of Troy. Homer might well have been astonished to learn that his poem would be turned into a cruise named “Journey of Odysseus: Retracing the Odyssey through the Ancient Mediterranean.” The elegant Corinthian II departs from Athens and tracks Odysseus’s journey through historical sites across Greece, Turkey, Malta, and Italy. Adventures include seeing the islands Odysseus visited, the ancient city of Troy, and the Phlegraean Fields outside Naples, where Odysseus encountered the cyclops. Suggested attire is country-club casual.

Photoshop Fling 5 Cruise
The Geek Cruises empire, based in California’s Silicon Valley, has built a solid reputation by booking educational nerd trips. One of their most popular is the Photoshop Fling 5, which sails the Caribbean while instructing passengers on the intricacies of the popular Adobe software. As Holland America’s 1,800-capacity MS Zuiderdam glides through a serene tropical paradise, guest speakers such as Marty Grivjack and Deke McClelland present classes like “Illustrator and the Beauty of Vectors” and “Smart Sharpen, Smart Objects, and Smart Filters.” Onboard Wi-Fi is provided (that’s 802.11b). Cabins have only one electrical outlet, so passengers are encouraged to pack their own power strip. Unlike most cruise brochures, the Geek Cruises website offers extensive information about all types of vaccinations and immunizations.

Hogs on the High Seas Rally Cruise
Each year, ports in Mexico, Alaska, and the Caribbean are invaded by a miniature Sturgis rally of hard-partying bikers. Cruises can accommodate as many as 1,000 people and are typically sold out 12 months in advance. Although the majority of guests are American V-Twin riders, non-Harley owners are also welcome. Onboard games and events range from prize raffles to pirate biker bingo and contests for best beard, best topless man, and best female “treasure chest.” The crowd-pleasing Belly Smacker contest awards a prize for the best belly flop into a pool: “Extra points awarded for redness of body parts and the oooohing of the crowd.” Organizers urge guests to wear their leathers for formal dining, because even the waiters will be wearing biker shirts and leather jackets.