World's Great Animal Migrations
David Fleetham / Alamy
Green Sea Turtle Migration, Costa Rica
Thousands of endangered green sea turtles enact an extraordinary annual migration ritual—by returning to the same remote stretch of Costa Rica's northeastern coast where they were born in order to lay eggs of their own. On the beaches of Tortuguero National Park, dozens of turtles haul themselves ashore each night to laboriously dig nests in the sand and deposit their precious eggs, before slipping exhausted back into the sea.
When to Go: June and July.
How to Get There: GAP Adventures runs multiday eco-trips and voluntourism programs in Tortuguero; both include guided hikes and boat tours in the park, educational talks about turtle conservation, and night patrols to see the turtles digging nests (from $399 per person).