“Visitors to the Philadelphia Zoo might want to beware of stray cats: A new enclosed passageway allows lions and tigers to roam outside their exhibits. Humans, though, can safely gawk at the predators traveling along Big Cat Crossing. The protected, open-air path snakes above the felines' habitat to an archway over the zoo's main promenade and ends at a viewing spot along a lake. The concept for the catwalk unveiled Wednesday, May 8, 2014 stems from the increasingly common practice of animal rotation, which lets animals take in new stimuli while visitors encounter them in unexpected places”. – Associated Press

An Amur tiger walks over the new Big Cat Crossing as visitors look on at the Philadelphia Zoo in Philadelphia, Pennsylvania May 7, 2014. The new animal exploration trail experience called Zoo360 of see-through mesh trails enables animals to roam around and above Zoo grounds. (Photo by Charles Mostoller/Reuters)

An Amur tiger walks across a passageway after a news conference at the Philadelphia Zoo, Wednesday, May 7, 2014, in Philadelphia. (Photo by Matt Slocum/AP Photo)

An Amur tiger walks over the new Big Cat Crossing at the Philadelphia Zoo in Philadelphia, Pennsylvania May 7, 2014. (Photo by Charles Mostoller/Reuters)

An Amur tiger walks across a passageway after a news conference at the Philadelphia Zoo, Wednesday, May 7, 2014, in Philadelphia. The see-through mesh pathway called Big Cat Crossing is part of a national trend called animal rotation that zoos use to enrich the experience of both creatures and guests. (Photo by Matt Slocum/AP Photo)

Owen Berk, 3, interacts with an Amur tiger inside the new Big Cat Crossing at the Philadelphia Zoo in Philadelphia, Pennsylvania May 7, 2014. (Photo by Charles Mostoller/Reuters)

An Amur tiger walks across a passageway after a news conference at the Philadelphia Zoo, Wednesday, May 7, 2014, in Philadelphia. (Photo by Matt Slocum/AP Photo)

An Amur tiger walks over the new Big Cat Crossing at the Philadelphia Zoo in Philadelphia, Pennsylvania May 7, 2014. (Photo by Charles Mostoller/Reuters)