Warren Stortroen, Earthwatch volunteer. — Courtesy Everett Collection, American International Pictures/Getty Images

Does sitting on the beach all day bore you? Are you sick of tour guides?

See also: How to find the right volunteer vacation.

How about a vacation that puts you to work, while exposing you to some of the world's most exotic places and eye-opening people? These kinds of immersion vacations aren't just for the recent college grad. In fact, half of all travelers with Global Volunteers, one of the largest volunteer tourism groups, are over age 50. The following volunteers said, "Yes, sign me up!"

Warren Stortroen, Earthwatch volunteer

It was his fourth trip to Mexico as an Earthwatch Institute volunteer, and so as his fellow travelers got a crash course in paleontology, Warren Stortroen embraced his inner Indiana Jones and headed out on his own expedition.

Near a dry riverbed he found small pieces of armor plating called scutes. "I was pretty sure they were from a prehistoric animal," says Stortroen. The research scientist leading the Earthwatch Mexican Megafauna expedition agreed: Stortroen had discovered a glyptodon, an ancestor of the armadillo, which in its day stood about 4 feet tall and was as big as a small car.

This was five years ago, when Stortroen was 74 years old and already an Earthwatch addict. In 15 years, he has been on 66 expeditions helping scientists conduct research involving paleontology, archaeology, endangered species, climate change and ocean health. He has studied dolphins in Vonitsa, Greece; worked shoulder-to-shoulder with archaeologists in Turks and Caicos Islands and helped save the endangered Australian bilby in Australia's Red Desert. He recently returned from the Amazon River and soon will be leaving to study wildlife and wine in Bordeaux.

"I used to do science museum tours where we went to interesting areas, but people were always just showing you things and telling you about them," says Stortroen. "Once I got involved with Earthwatch, I no longer just wanted to look at things. I wanted to do them."

Jay and Joyce Rush, Habitat for Humanity

They call it "Infectious Habititis," and it's a condition Jay and Joyce Rush developed almost 10 years ago. Jay Rush took an early retirement, and the couple sold their York, Pa., house, moved into their RV and hit the road helping to build homes for people in need.

Next: Building homes on volunteer trip to Belize. >>