Do fighting in a joust, jamming to your favorite polka band and trying to solve a murder sound like a typical leisurely cruise? For folks aboard theme cruises, they are getting exactly what they paid for. Whether you fancy astronomy, espionage or the ukulele, chances are there is a cruise out there for you.

Steve Wallach, President of Entertainment & Travel Alternatives, Inc (ETA) who has been hosting theme trips such as motorcycle and bluegrass cruises for 13 years, says they are more successful than ever, though he says the business is getting more competitive each year. "Everyone wants to offer the most memorable trip, because that's what it's all about, taking a cruise that will stand out." Adds Justin Seidenberg, of Kiqstart Music who produces a Pink Floyd-themed cruise, "People now are looking for more than just a concert or convention, they want a full-blown, once-in-a lifetime experience."

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As cruises rise in popularity, liners are taking full advantage of unique niche hobbies, lifestyles and intellectual pursuits. From quilting to renaissance fairs, some theme cruises are meant to enlighten while others are meant to be just plain fun. The PBS program Antiques Roadshow partnered with Travel Dynamics International, and hosts cruises where passengers can dig for antiques with archaeologists. Two such cruises are scheduled for this year: one to the Great Lakes, the other to Greece and Turkey.

Theme cruises are good for single travelers or shy people because they will immediately be placed amongst a group of people who share the same interests. Some cruises even offer an option to bunk single travelers together. Wallach says that "theme cruising is all about sharing a common ground with other people and building a camaraderie with friends that you may see year after year on the same trip."

One of the benefits of taking a theme cruise is the opportunity to be able to talk one-on-one with field experts. Espionage enthusiasts can take a top-secret mission to Istanbul on the SpyCruise and learn about Cold War and Soviet spy missions from retired (and some still active) intelligence officers.

These cruises also try to attract a wider type of crowd. Amanda Densmore, of Expert Travel Concierge, says "Theme cruises are not only interesting for experts but they are a great way for novices to begin exploring new interests." The only requirements for attendance on a theme cruise are the desire to have fun and socialize.

Although not a requirement, dressing up in costumes often hel[s for getting in the theme mood is . Wallach says, "Most guests on our cruises really get into the whole theme and dress the part. " In June, Princess Cruises embarks on its Renaissance Festival cruise from Vancouver to Alaska and on hand, ready for the jousting tournament, will be plenty of costumed knights and nobles.

So whether your first love is eclipses or ukuleles, there's likely a cruise just for you.

See our slideshow of Oddball Theme Cruises '09.