Count turtles in the Seychelles

It's not cheap, but it is probably the ultimate experience for a scuba-diving enthusiast. This is a rare opportunity to be part of a scientific research team, diving the reef as you collect data on coral and fish, and taking part in vital surveys of whale sharks, turtle, octopus and lobster species. Be prepared to spend the first fortnight in intensive teaching sessions.
Price From £1,745 for five weeks excluding flights; departures on 2 Jul, 6 Aug, 1 Oct, 5 Nov
Book it responsibletravel.com/Trip/Trip101021.htm

Help street children in Peru

If you can handle a hammer, you can make a practical difference to the lives of streetchildren in Peru. The Vine Trust's working parties offer basic manual labour to help build and maintain centres for abandoned boys and girls, in a country where thousands of children are purposefully "lost" by parents who can no longer afford to care for them. Your two-week visit will take in the capital, Lima, and one of the charity's more remotely located centres – which likely means a jungle expedition. And you can opt to stay on to visit Macchu Picchu and the Inca Trail.
Price £900 for two weeks excluding flights; £300 goes to building materials
Book it vinetrust.org/workparties

Crew a tall ship

Sailing a 55ft ship isn't something many people can claim to do – and that's the point of the Jubilee Sailing Trust's holidays. It operates a buddy system which pairs able-bodied and physically disabled crew members in an environment so challenging and unknown that no one has an advantage. Involved in every part of running the ship, from helming to scrubbing the decks, you can take a day trip to Jersey, a week-long sail along the coast, or a longer expedition in the Mediterranean or the Caribbean.
Price From £135 for a daysail to £1,350 for a month-long passage to Antigua
Book it jst.org.uk

Join a South African village

The rural village of Mapoch, 40km outside Pretoria, was hit hard during the apartheid years: villagers were forced from their land to an area with no infrastructure and little employment. People and Places UK, which was named "best volunteering organisation" in the Responsible Tourism Awards 2009, has worked with the Mapoch's Ndebele community to set up various businesses, amenities and education projects. Whether your skills are practical (construction, crafts, catering) or more cerebral (IT, teaching, business and marketing), they can find a way for you to benefit the village.
Price From £1,295 for four weeks, excluding flights
Book it responsibletravel.com/Trip/Trip900591.htm

Care for Cambodian orphans

Visitors are more than welcome – they're positively encouraged at this small orphanage in rural Cambodia. Caring for around 50 children of all ages, the orphanage feels like a large family home but also offers a range of educational and vocational opportunities, including a workshop, beauty salon and an arts and crafts centre. Volunteers help to widen the children's horizons even further with new skills and languages. Accommodation is at a large house in the centre of the town; Phnom Penh is an hour and a half away, and there are plenty of opportunities for sightseeing.
Price From £399 for two weeks excluding flights

Book it thepodsite.co.uk/projects-destinations/cambodia-orphanage.html

Preserve your environment

Whether it's building hiking trails in Iceland's National Parks or coppicing on the banks of the Kennet, BTCV (the British Trust for Conservation Volunteers) runs holidays that offer a unique chance to get back to nature. There are more than 200 holidays a year on offer; accommodation can range from a humble tent to a luxury cottage, depending on your preference and budget, and food is included. You'll need to arrange your own travel – and expect to cook your own meals.
Price Current deals include £180 (for seven nights) protecting butterfly habitats in Dartmoor; £570 (10 nights) cultivating orchards in Romania.
Book it btcv.org

Coach sports in Brazil

Infected by World Cup fever? Responsible Travel's football break in Brazil offers you the chance to play the beautiful game in the most obsessed nation on earth. In one of the poorest areas of Rio you'll help at a club specially created for children who would otherwise be on the streets: no coaching qualifications necessary, just an enthusiasm for the game that matches theirs. And it's not just footy – other projects cover a wide range of sports from athletics to volleyball and dance to martial arts.
Price From £795 for 14 days excluding flights
Book it responsibletravel.com/Trip/Trip902407.htm

Run a stately home

For variety and value, few organisations can match the National Trust's working holidays, where you help to protect some of Britain's most beautiful countryside and historic houses. For £90 for a week, staying in hostel-style accommodation, the Trust offers hundreds of different activities, from goat-herding and dry stone walling to archaeology and children's work; some also provide the opportunity for outdoor pursuits like surfing and sailing. New projects this year include tending the medieval knot garden at Norbury in Derbyshire and helping to run a food fair at the romantic Godolphin estate in Cornwall (pictured, above left).
Price From £55 for a weekend
Book it nationaltrust.org.uk/workingholidays

Wash an elephant in Thailand

You don't have to join the circus to work with elephants. At a wildlife rescue centre in Tha Yang, Thailand, volunteers work alongside professional "mahouts" (keepers) to walk, water, feed and bathe the animals. The six domesticated elephants here have been rescued from the city streets where they were used for begging; with up to 10 others, you can spend a week or three getting to know these magnificent creatures. It's not all clearing dung: Bangkok is two and a half hours away, and there are tropical beaches close by.
Price From £425 for one week, excluding flights
Book it thepodsite.co.uk/projects-destinations/elephant-care.html

Join a blind person in an adventure

Blind filmmaker Amar Latif came up with Traveleyes' unique tours, in which blind and sighted travellers holiday together in equal numbers. In return for a discounted holiday, you'll use your eyes to share the experience with your companions, whether it's Turkey's Turquoise Coast, the golden beaches of California or Florence's majestic Campanile. Traveleyes has won Latif several awards, and its customers – both sighted and blind – keep coming back.
Price From £499 for 8 days
Book it traveleyes-international.com