Toni Ruttimann left his Swiss hometown at 19, headed off to Latin America, and ended up filling a niche by helping and teaching locals to build foot bridges across rivers that were otherwise hard to get across. From Wikipedia, "To date, December 21, 2012, Rüttimann and his local teams have built 607 bridges, serving over 1.3 million peasants in Latin America and Southeast Asia. He works independently, and for free."
Here is one account of a bridge he helped build in Indonesia.
Another feature profile with lots of pictures at this pdf page.