Preserving historic sites and digging up ancient ruins are popular activities for volunteer vacationers. The projects often need volunteer help, as funding for these endeavors does not always match their importance. For example, you might work on the preservation of the battlefield at Antietam, Maryland, one of America's iconic historical sites.
The range of archeological digs, building repairs and maintenance projects available to volunteers is practically unlimited, and could take you almost anywhere in the world. You could restore a Buddhist monastery in Nepal or excavate a Roman villa at Pottio Del Molino in Italy. Wherever you go, you'll combine healthy physical work with a hands-on learning experience.