This zoo was one of the first in the country to feature open, natural environments for its animals. Loop trails and a miniature train wind amid its 125 park-like acres, home to 1,500 mammals, birds and reptiles. Habitats include the four-acre Arctic Ring of Life (the largest polar-bear exhibit in the world) and the new National Amphibian Conservation Center. Inside a renovated 1928 glass-domed bird house, the Wildlife Interpretive Gallery incorporates a butterfly garden and an aquarium.