The Port: Antarctica

Why you'd leave the comfort of your stateroom, we'll never know. But you can stay overnight onshore on the White Continent in a two-person tent, or out in the open in nothing but an insulated sleeping bag (talk about bragging rights). You'll fall asleep to the sounds of heaving glaciers and perhaps whales spouting and feeding in the bay. Don't forget to put on your long underwear — and wake early to see the amazing sunrise.

Who Offers It: Hurtigruten offers overnight camping, often included in the price of the cruise.

Port: Cabo San Lucas, Mexico

Make no mistake: This is an extreme two-hour experience. The glass-floored gondola ride alone, high over the canyon at Wild Canyon Ekopark, is enough to make us faint. Follow that up by launching yourself into the abyss — fully harnessed, of course.

Who Offers It: Cabo San Lucas Tours offers bungee-jump time slots specifically for cruise passengers ($93.50 per person; www.cabosanlucastours.net).

Port: Funchal, Portugal

Yes, there's a basket involved, but this is no picnic. Picture yourself zipping down a Madeira street in a wicker rig. These out-of-the-ordinary rides date to the mid-1800s, when residents began using toboggans to transport goods down the hills and into the town center. Today, you can hop into two-seater sleds — on roads with traffic — as guides do their best to steer clear of the looming stone walls.

Who offers It: Cruise lines that visit Funchal such as Celebrity Cruises and Regent Seven Seas offer the toboggan ride as part of a tour that also takes you around Madeira in a cable car (from $16.50 per person).

Port: Ketchikan, Alaska

Yes, during summertime the water temperature hovers in the mid-50s; but during this three-hour tour you'll be outfitted head to toe in a wetsuit and sufficiently distracted from the chill by the colorful creatures (sea stars, sea cucumbers, urchins) and plant life in the shallow tidal pools.

Who Offers It: Princess Cruises offers the Mountain Point Snorkeling Adventure with Snorkel Alaska (from $108 per person)

Port: Tauranga, New Zealand

Bomb down a scenic mountain in New Zealand in a three-wheeled contraption that's part toboggan and part go-cart. The twisting trails zip through redwood forests as you are propelled by gravity — and your own bravery. (The tracks are paved, and riders wear helmets and have full control over speed and direction.)

Who Offers it: Skyline Luge in Rotorua offers 3 courses to try, as well as a gondola ride up the mountain (from $28 per adult, $14 per child, www.skylineluge.com).

Port: Koper, Slovenia

You'll accompany mushroom-seeking hounds and their masters on a search for these gastronomic delicacies. This six-hour adventure begins with a journey into an isolated forest in the Dragonja Valley (via 4x4 vehicle) and ends when a chef at the Brič Winery Estate transforms your truffle haul into a gourmet lunch.

Who Offers It: Celebrity Cruises offers this excursion as part of its Celebrity Exclusives program (from $398 per person).

Port: Philipsburg, St. Maarten

Rent a Fatboy, Softail, or V-Rod and set out on the open road to explore the Caribbean island of St. Maarten — from beaches to villages and everything in between — on this self-guided tour, which can last more than six hours.

Who Offers It: St. Maarten Cruise Excursions offers the Harley in Paradise Tour ($181 per person, including helmet, insurance, map, and instructions; www.stmaartencruiseexcursions.com).

Port: Bucharest, Romania

Explore 14th-century Bran Castle, which is intimately linked to the legend of Dracula. This fortress was used by Vlad the Impaler as a base for his forays into the Transylvanian countryside.

Who Offers It: Viking River Cruises and Avalon Waterways offer this three-day cruise extension (prices vary).