Man has always held a certain fascination with the creatures of the wild. Since ancient times, humans have been creating new and innovative ways to observe and interact with all manner of wild animals.
Modern zoos often get a bad rap, seen as places that take animals out of their natural habitat and cage them for the pleasure of spectators.  But many internationally renown zoos are at the forefront of animal preservation, and showcase the natural beauty and diversity of the world's wildlife in exciting and stimulating ways.
Here are some of the world's best that are worth traveling for.

Berlin Zoo - Berlin
With over 14,000 animals on exhibition, Berlin Zoo ranks among the largest zoos in the world. Spanning an area of roughly 74 acres, this huge compound attracts over 3 million visitors annually. The zoo was originally constructed in 1844 and thrived for decades before coming close to decimation during the Second World War. Today, the zoo contains a variety of large open habitats as well as a magnificent aquarium containing some 9,000 species of fish, amphibians, reptiles and host of other colorful creatures.

Bronx Zoo - New York City
With over 4,000 animals housed within 265 acres of New York City terrain, the Bronx zoo is the largest metropolitan zoo in the United States. Since its establishment in 1899, the park has expanded to include numerous state-of-the-art enclosures and exhibits, such as the 6.5-acre Gorilla Forest, and Tiger Mountain, a detailed recreation of Russian woodland where a streak of Siberian tigers roam. The enormous Wild Asia complex plays host to Asian elephants, Indian rhinos and various other creatures which can be viewed on a sightseeing monorail trip.

Singapore Zoo - Singapore
A true pioneer of the industry, the Singapore Zoo was the first to introduce an "open zoo" concept, which presents no visible barriers between the animals and the visitors. Most enclosures are separated behind moats, vegetation or other natural features, though glass walls have been installed to house some of the park's more ferocious residents. Aside from the up-close encounters available at the Primate Kingdom, and Reptile Garden, the zoo showcases magnificent underwater views of polar bears, sea lions and penguins.

San Diego Zoo - San Diego
The world-famous San Diego Zoo is an expansive 100-acre complex housing a 4,000-strong collection of some of the most exceptional and rare creatures on Earth. In recent years, this ever-evolving zoo has expanded to include cutting-edge animal enclosures like the Polar Rim and Elephant Odyssey. The zoo's most celebrated residents are housed at the Giant Panda Research Center, where staff members have had enormous success in breeding these endangered creatures.

Tiergarten Schonbrunn - Vienna, Austria
Vienna's Tiergarten Schonbrunn offers one of the most unique and refined zoo experiences in the world. Originally constructed around the turn of the 17th century, this Austrian landmark is often considered as the world's first modern zoo. The zoo was founded by the husband of Empress Maria Theresa and was often frequented by members of the Hapsburg dynasty for their summer retreats. Today still retains much of its original beauty and tranquil charm with magnificent 18th century buildings and a stunning botanical garden.

Courtesy of Mark Rosenthal.

'I don't know how Singapore or San Diego got added on this list of "worlds best?"   I think San Diego is always just automatically given a spot, simply because it is San Diego.  I guess it is what you are into.  I go for history, not gunnite Buddha temples.'