United States - San Diego Zoo

The San Diego zoo is located Balboa Park, just north of the city centre.It was originally opened by Dr Harry Wegeforth in 1916 and is one of the largest zoos in the world with over 4,00 animals of more than 900 different species set within a 100 acre space of land. The cool, sunny maritime climate is well suited to many  animals which is why there is such a large number of different birds, mammals and reptiles. The grounds of the zoo are maintained as a arboretum. There are around 15,000 trees in the park, including palms, pines and eucalyptus, the most famous tree in the park is the Moreton Bay fig, located near the National History Museum and planted in around 1915. 

Due to the zoos large size, other than walking, there are two ways of getting around the zoo. The first being a guided tour bus that traverses 75% of the park. The other is a overhead gondola lift. the gondola lift provides a quick and efficient way of getting from one end of the zoo to the other. 
San Diego Zoo is arguably the worlds best zoo, and if you ever get a chance to visit, it is highly recommended.