Styled after Sansovino's 16th-century Library at St. Mark's in Venice, this impressive structure, built in 1905, looks out on the body of water known as the Lullwater. It now houses the Prospect Park Audubon Center, where you can learn about nature in the park through interactive exhibits, park tours, and educational programs especially for kids. On a nice day, take a ride on the electric boat or rent a pedal boat and head out onto the Lullwater and Prospect Lake. Or sign up for a bird-watching tour to see some of the 200 species spotted here. The café is always good for a break. COST: Audubon Center free; electric-boat tours $3; pedal boats $10 per hr. Subway: 2, 3 to Grand Army Plaza; Q to Prospect Park.