It's a phenomenon that has been watched firsthand by Sue Badyari, who started adventure travelling "before the age of 14" and now organises adventure travel trips in her role as chief executive of Australian-based World Expeditions.
"Over the 20 years I've been involved in the industry I've seen an enormous amount of change," she says.
"When I started it really was the hairy-chested bushwalkers who were the adventure travellers.
"Nowadays the definition is much broader than that. Adventure travel now includes everything from as soft as a luxury safari in Africa to scaling some of the highest peaks in the world.
"In the early days adventure travellers were people who went bushwalking and camping in their weekends and so were used to looking after themselves in that sort of environment.
"Now we have a lot of customers who would define themselves as adventure travellers because they have this great passion to explore the hidden corners of the world, but prefer the comfort of a hotel at night."
Badyari says it is this soft adventure travel which is the big growth area as baby-boomers discover the joys of adventure tourism.
"I believe we're really only scratching the surface of it. There's a lot more to come in the next decade."
That growth, she says, has also led to changes in the adventure travel industry itself.
"In the past, most adventure travel companies were owned and operated by people who were adventure travellers and had a great empathy with the places they visit. But now there are increasing numbers of people coming into the industry who are more focused on the business side and whose aim is primarily to make money."
All of that creates huge challenges for the adventure travel industry.
How do you cope with large numbers of tourists while preserving a destination's uniqueness? How do you provide comfortable accommodation while protecting an area's wildness? How do you preserve a culture while allowing increased contact with the outside world?
Badyari believes that can be achieved through the practice of responsible tourism, almost a cliche these days but something which World Expeditions has espoused since it was founded 30 years ago.
"In some ways," she says, "it's a little dismaying to find responsible tourism suddenly being marketed as an entirely new brand of tourism. But at the same time it is good it's becoming more common because the places we travel to are often fragile environments."
World Expedition's brochure defines responsible travel as requiring "true sustainability ... specifically to ensure that the natural and cultural values of the regions in which we operated are not undermined."
That means, says Badyari, that the company has strict protocols when designing trips. "When we go into new areas we work through our process, talk to the local people, and plan for a sustainable tourism programme right from the outset.
"That may mean trips have to cost a little more because of the need to avoid depleting cheap local resources. It usually means providing training for local people so they can benefit from the tourism.
"Longer term, it often means assisting with the education of local children.
"If you set down the right foundations from the outset then it can work really well for the communities and the environment that you are travelling through. But if it isn't done at the outset and exploitation does occur then it's much more difficult to try to wind things back at a later stage."
That sounds all very well, but with so many adventure travel companies all looking for special places to visit, is it really possible to stop them being commercialised?
Fortunately, Badyari says, sustainable tourism is now "very much part of the landscape and it's something most adventure travellers now expect", although she acknowledges that "occasionally it is more of a marketing tool to which lip service is paid".
But, ultimately, if a company like World Expeditions is unhappy at what is happening in a particular area, "if it gets to a point where trails become too commercial and we no longer have any control over what is happening, despite whatever lobbying or development work we might be doing, then we'll simply move away".
As a result, the company is always on the lookout for new destinations.
"We think of ourselves as innovators. We try to anticipate where the market is going to go rather than following others.
"Some companies talk of going off the beaten track but when you look at their itineraries they're very much on the beaten trail. But we have a very strong philosophy of following the path less travelled and often you'll find we are the only company operating on the trails we use."
New destinations, Badyari says, come mostly from suggestions from the company's staff who are all enthusiastic travellers and readers of travel writing.
"It just takes one good idea. Normally we'll send someone off to do the research and try to find a local operator we can work with. If it works out we'll put it in the brochure.
"We often find places and have them in the brochure for two or three years without getting the numbers to get a trip away. But we persist with them because we believe the market will go there in the future."
SECRET TRAILS
If you really want to follow the path less travelled, and go somewhere your friends and neighbours haven't been, where is there left to go? Sue Badyari, has a few suggestions:
* The Kamchatka Peninsula in the far east of Russia.
* Spitsbergen in the high Arctic.
* Trekking in Bhutan or the eastern Indian Himalayas.
* The Tian Shan Range in Central Asia.
* Cycling through rarely visited parts of China.
* Walking the Iceland circuit.
* Parts of the Galapagos Islands where the tourist boats don't usually go.
* Exploring the highlands of Ethiopia.
"There are still places out there which are in the same league as Angkor Wat or the Pyramids but hardly anyone knows about them," Badyari says.
"Go there, and 99 per cent of the time there'll be no other travellers."
