Queen Mary 2
Line: Cunard
Passengers: 2,592
Itineraries: Worldwide
Perhaps the QM2's enrichment programs earn such high praise because there aren't any distractions when you're 1,500 miles from land on one of the ship's transatlantic sailings. Or perhaps it's because Cunard recruits a rotating lineup of diverse and fascinating lecturers such as novelist Margaret Atwood and intelligence analyst Glenmore Trenear-Harvey. Overachievers can also enroll in acting workshops given by London's Royal Academy of Dramatic Arts, pick up some card tricks from the onboard bridge lecturer, or study the skies from inside the planetarium (800-728-6273; cunard.com; six-day trans-atlantic trip from $1,445).

River Countess, River Duchess
Line: Uniworld Grand River Cruises
Passengers: 134
Itineraries: Danube, Rhine rivers
The benefits of cruising are evident in an itinerary like these sister ships' Eastern Europe Explorer, which visits no fewer than seven countries in 16 days—along a stretch of the Danube ignored by most other riverboats. Lecturers from local universities board the ship and talk about, say, the Balkans' transition from the Ottoman Empire through communism to the present day. Onshore excursions to sights like a Roman ruin near Belgrade and the Parliament Building in Budapest are done via personal audio systems; the guides speak into transmitters and the passengers wear headsets, so they don't have to travel in a pack to hear the commentary (800-733-7820; uniworld.com; 16-day Eastern Europe Explorer trip from $4,120).

Seven Seas Mariner
Line: Regent Seven Seas Cruises
Passengers: 700
Itineraries: Worldwide
Care to study photography, yoga, or French cuisine while at sea? The courses available during the Mariner's Circles of Interest voyages are as diverse as the ship's destinations, and dig deeper into the subject matter—food and wine, architecture and literature, health and wellness, environmental sustainability—than most onboard enrichment programs. You'll pay a few hundred dollars extra to be in a group of up to 30 passengers taught by experts including oceanographer Jean-Michel Cousteau, Dr. Deepak Chopra, and Le Cordon Bleu-trained chefs. Each topic is addressed in port as well as on board, so an oenologist's cruise might visit a vineyard that isn't normally open to the public (877-505- 5370; rssc.com; seven-night Alaska trip from $4,195).