Where: National parks and other public lands, from Maui to Martha's Vineyard
What: The Sierra Club runs about 90 service trips each year, with participants building trails, repairing meadows, and helping with archaeological surveys.
Duration: One week
Volunteers pay: $350 to $600, which covers meals and accommodations ranging from campsites to rustic lodges (sierraclub.org/outings/national/service.asp)
O is giving away 5 amazing trips! You'll swim with sea turtles and spend your days on white sand beaches at Le Meridien Tahiti and Le Meridien Bora Bora.