It felt as if we had the jungle to ourselves.

As we explored Costa Rica's Corcovado National Park, we spotted rare birds, spider monkeys — even a sloth and her infant — among the trees of the rainforest.

It was one of many experiences I had on an expedition cruise with 32 passengers aboard the Greg Mortimer, operated by the Australia-based Aurora Expeditions.

During the 13-day voyage, we crossed the Panama Canal and snorkeled amid hawksbill turtles in Panama's UNESCO-protected Coiba National Park. We also met members of the indigenous Embera tribe deep in Panama's thick jungle. 

Built for polar regions, this was the ship's first foray into tropical waters, as companies like Aurora are responding to the growing demand for expedition cruises.

Instagram posts — which often showcase trips to Antarctica — may have given expedition cruising more publicity, but this form of cruising isn't new. 

The evolution of expedition cruising

U.S.-based Lindblad Expeditions started taking travelers to Antarctica and the Galapagos Islands in the mid-1960s. 

The company specializes in expedition cruises, which differ from conventional cruises in that they focus on exploring isolated, less visited or inaccessible destinations. Smaller ships also allow itinerary flexibility, which means the captain can slow down for guests to observe polar bears or a whale shark.

Aurora Expeditions has been plying Antarctica's frozen waters since the cruise line first leased rudimentary Russian icebreakers to reach the icy continent in the early 1990s. 

"Bathrooms were shared, and we'd string our clothes across the cabins to dry," said Bronwyn Stephenson, a veteran Aurora expeditioner.

With its spacious cabins, plush library and lecture theater, the Greg Mortimer is a far cry from these original expedition cruise ships. 

Today, there is stiff competition among expedition cruise lines to launch more technologically advanced vessels and to secure onboard talent. Lindblad recently recruited underwater archaeologist Mensun Bound, who has discovered ancient shipwrecks, and former NASA chief scientist Robert Bindschadler, to educate passengers.

Demand since the pandemic

Aurora Expeditions' chief marketing officer Hayley Peacock-Gower said there has been a strong shift to immersive, experiential travel since the pandemic. As travelers demonstrate burgeoning interest in nature, wildlife and cultural tourism, expedition cruise lines have answered the call with more and varied itineraries.

Noah Brodsky, chief commercial officer of Lindblad Expeditions-National Geographic, described expedition cruising as the "breakout travel trend of the decade."

"There's something truly special and transformative about experiencing remote destinations alongside a small group of like-minded people," he told CNBC.

Bookings through the roof

Lindblad recorded its biggest-ever booking day on Jan. 3, racking up some $5.6 million in sales, according to a company representative.

In-demand destinations this year include Alaska, the Galapagos Islands, the Arctic and Antarctica, according to the representative, while interest to Costa Rica is up 54% from 2019.

The company also launched new routes to Greenland, French Polynesia and Western Australia's Kimberley region.

James Cole, founder of the U.K.-based cruise agency Panache Cruises, said expedition cruising saw the most growth in the cruising sector in the past decade — expanding from about 67,000 passengers in 2012 to 367,557 in 2022.

"An increasing number of people no longer want run-of-the-mill holidays," he said. "People crave adventure … there is a certain amount of romanticism here which harks back to the time of great explorers like Hillary, Cousteau and Shackleton."

Who takes expedition cruises?

Most of the demand for expedition cruises comes from the over-55 age group, namely the semi-retired and retired who have the time and resources, Cole said. 

But he noted: "We are seeing more families entering the market."

Gen Xers and millennials represent a smaller percentage of clients. "It is the 'experience' and 'adventure' which is driving their interest. The cruise aspect is really a secondary dimension," Cole noted. 

Expedition cruising is also a good option for the growing number of solo travelers. 

I hadn't visited Central and South America before, mostly because deciding which countries to visit and planning an independent trip seemed overwhelming and complicated. As a woman, I was concerned about safety too. The Aurora cruise was the ideal introduction, with shore excursions led by onboard experts and engaging local guides. 

Higher fares, longer cruises

Plusher ships, onboard experts and fewer passengers translate to higher fares than conventional cruises. Expedition cruises often start at around $1,000 per person per day. Trips typically last eight to 15 days — though some can take a full month.

While conventional cruises can host thousands of people at once, companies like the polar micro cruising company Secret Atlas can take as few as 12 cruisers at a time.

But a push for more comfort and luxury in the industry is causing some expedition cruises to get bigger, said company co-founder Andrew Marsh.

"Unfortunately, this has meant the new expedition cruise ships have become larger and the expedition experience itself has been sacrificed," he told CNBC. 

Environmental and cultural impact

Though they're smaller in scale, expedition cruises have faced criticism for polluting oceans, introducing microbes to sensitive environments, and colliding with large mammals like whales. 

To combat some of these issues, the luxury travel agency Abercrombie & Kent is chartering the luxury icebreaker Le Commandant Charcot for a North Pole expedition next year.

"To reduce emissions to the lowest possible level, this Ponant ship uses LNG as a fuel," said the company's product development and operations vice president Stefanie Schmudde. "The vessel also uses hybrid operation, with batteries to handle load fluctuations."  

In February, Aurora and Sylvia Earle led an Antarctic climate expedition on a ship named after the renowned oceanographer. The aim was to raise public and government awareness of the Antarctic's environmental importance. 

Aurora Expeditions' Peacock-Gower said the company worked with 117 climate ambassadors, aged 12 to 88, to formulate eight climate resolutions that are designed to achieve net-zero emissions by 2035. 

"Travel is always the best educator, and we offer the chance to enrich our passengers' curiosity … on and off-ship," she said.