More than 20% of Culebra is part of a spectacular national wildlife refuge, which was signed into law more than 100 years ago. Most of it lies along the coastline, including more than 20 cays. Home to three different ecosystems, the refuge is a habitat for endangered sea turtles and the largest seabird nesting grounds in the Caribbean. For visitors, it's a place for hiking, birdwatching and secluded beaches. The US Fish & Wildlife Service office has maps and information.