This couple spent a month in Transylvania helping to build organic houses. This project used straw bales, timber frame, clay plaster, stone and thatch roofing. The materials will differ according to the climate, culture, etc. This is a great way to learn natural building for free, because you learn by doing without an overly long, hard schedule.
You can search for volunteer opportunities in the area of your choice on natural building workshop calendars, facebook, natural building websites, and various websites such as Workaway, WWOOF, HelpX, Farmstays and Reach Out Volunteers. If you enjoy this sort of thing you can keep doing it from place to place and travel the world for free.
Building organic houses in Transylvania – Workaway