Trek through the jungles of the Amazon, cruise to Antarctica to hang out with the penguins or mountaineer up Everest. The Angkor Wat temple complex in Cambodia, closed to foreigners due to war until 2000, has since done a booming business. Additionally, the old adventures are becoming new again as 19th century innovations like the Orient Express are restored and reopened.
The Peace Corps has long been a volunteer travel opportunity. But now thanks to the Internet there are a multitude of small nonprofits around the world that can solicit volunteers directly. The most popular volunteer activities are teaching English and working in orphanages, but almost any skill can be used. An increasing number of retired businesspeople are devoting time to mentoring small-business owners in the developing world.
Local governments have begun merging conservation projects with tourism, often using the profits to fund ecology projects. Dolphin Island in southern Philippines is a marine conservation and dolphin breeding program that offers tourists the chance to swim with the animals in the "wild," while help restoring an endangered population.
No longer just university-based exchange, study abroad vacations are now available in the form of seminars and short classes. Study micro-entrepreneurship in Nepal, massage at Wat Po Temple in Thailand, tea-making in India or martial arts in China. It's even possible for a group to privately contract a professor for a learning tour over summer vacation. An example is studying art history in the museums of Italy.
The global financial crisis reintroduced the idea of staying home for vacations, and gave it a new name: stacationing. Far from a suggestion that you should watch TV all summer, proponents of the stacation suggest that you treat your own area as if you were showing it off to out-of-town guests. Attend your own festivals and museums, take a guided architecture tour and eat at the famous local restaurant.