The Densu Delta Protected Area is a coastal wetland west of Accra, where lagoon, saltpan, and marsh habitats interrupt the city's spread. It is especially interesting for birdlife and for seeing how much ecology still survives at the edge of the capital.
This is not a manicured city park, so go with realistic expectations and local advice. Birdwatchers will get the most from it, but any traveller interested in Accra's coast beyond beaches and traffic will find it worthwhile.