There are so many company’s online who charge an absolute fortune, not including flights, to volunteer across the world and so few people who know that you can volunteer for free.

You don’t have to do that. There are also companies like WWOOF and Workaway that list hosts around the world looking for volunteers for a small annual fee and that’s all you pay.
I have used both WWOOF and Workaway, the former to volunteer on an organic vineyard in southern Western Australia and the latter to volunteer at the guest farm I spent three months at last year in South Africa.
I am using Workaway again to volunteer at three different places in Western Australia this year.

If you’re just coming out of high school, I highly recommend going to volunteer. You will learn so much about yourself and the world and grow in a positive way. You will learn new skills and may even discover your passion or realise that what you thought you wanted isn’t in the end.
If you’re at a cross roads in your life and you don’t know what to do with yourself except that you need to break out of your current funk, go volunteering! I’ve now volunteered in Thailand, Western Australia and South Africa.

If you are spending an extended period of time in a new country, volunteer, you get to learn the language and the culture much better than just wondering around like a tourist. You learn the best places to eat and shop and because you’ve learned their every day language, you are better respected when you go to restaurants and shops. All countries love it when you make an effort to understand and integrate their culture.
If you want a new career, volunteer. You get hands on learning for free and may even pick up a job while you at it, or at least develop a useful network of contacts in your future career. It also looks good on your CV or student application.

Volunteering is the perfect way to grow as a person and learn new skills, not to mention make some lifelong friends and memories.
