It's easy enough to say get someone else to pay for your travel. But it depends first of all on who you are, starting with your age. Younger people have a number of different ways of getting someone else to pay. But why should anyone pay an older person to go travelling around the world, unless he or she has some special experience that makes it worth sharing with others?
If you are older, no longer having the same energy as when you were young is only the first of your problems. Young or old, it depends above all on who you are, and whether you are interesting as a person. Another question is how you will be travelling, since there are different ways, with advantages and disadvantages to all of them.
If you are in your "working years," the most obvious way is having a job that requires you to travel whereas, if you're retired, you have to rely on your past experience. In either case, it still depends on what kind of job we're talking about. Most of us haven't much of a choice here: it's what we've got!
A few people, of course, have high-profile jobs to start with, a recent example of which is Dominique Strauss-Kahn, managing director of the International Monetary Fund, now the subject of scandal. Used to travelling first-class, he would stay with his family in exorbitant hotel suites all over the world and own similarly expensive apartments. Fine for him, one might think, but with the disadvantage that he knew little of the real lives of most ordinary people.
Airline crew see a great deal of the world but with little time to explore it. So do those working on cruise ships, at least for places on or near the sea, but largely for tourist destinations where, for as long as the ship is in port, "real life" is crowded out. Or, like myself, you can lead travel groups, but again largely to places visited by tourists, seeing little of everyday life there.
More interesting are the possibilities for living abroad, but it still depends on where. Diplomats and army officers can get stuck in undesirable locations, where they have to work hard and may have little chance to travel. On the other hand, my son and daughter-in-law have been temporarily transferred to Geneva, and are thoroughly enjoying the opportunity for travel in Europe and skiing during the winter. I myself have taken advantage of university sabbaticals, in my native England and the South of France too, where we were free to explore Provence and neighbouring areas for almost a year.
University research itself provides possibilities of attending conferences and travelling to libraries. With my interest in languages, I have often travelled to the former USSR (living in Leningrad for a year as a graduate student) and modern Russia, leading tourist groups there too. I have been several times to East and West Berlin, both before and after the "Wall." I have travelled all over Canada and the States, although always one is limited by the time for the conference itself and the reading in libraries.
I have also taught Elderhostel courses for my university and I am now interested in taking courses in which I can speak my languages and participate in the cultural life of another country, although I would probably have to pay for this myself. Another way of getting involved in the life of the country--although here again you might have to raise the funds to cover your expenses -- is to volunteer your services, particularly if you happen to be a doctor, nurse, or even a veterinarian.
And then of course, if you are young you can take a year off and do odd jobs to support yourself: working, and then travelling between jobs. My older son saw most of New Zealand that way, travelling by bicycle and finally volunteering as crew on a yacht sailing to Tonga.
Similarly, when I was younger I worked during my university vacations in Switzerland as a tour guide in a hotel, and later went to teach English in Sardinia. Both experiences provided the basis for my novel, Sardinian Silver. I combined my knowledge of a tourist hotel with living in a pensione with students who spoke only Italian -- since their regional dialects of Sard were mutually incomprehensible.
Many of these characters went into that novel, combined imaginatively with some of my own experiences. It is not an autobiography, but at that time I certainly experienced something of everyday life on the island, which then was very different. Not having a car wasn't really a disadvantage, since instead a colleague and I tried hitchhiking. It was so unusual that it worked.