The polar bear enclosure was built with wartime road blocks and pill boxes
Never before seen pictures taken by the family who created Chester Zoo have gone on display to mark the attraction's 75th birthday.
The zoo was founded by George Mottershead who helped create the North of England Zoological Society in 1934 to run the zoo.
During World War II, the zoo used wartime road blocks and pill boxes to build the polar bear enclosure.
An exhibition charting the zoo's development is on show by the aquarium.
Stephen McKeown, Chester Zoo's head of education, said: "George Mottershead was a visionary. He saw what good zoos could achieve, the difference they could make in the role of conservation and the importance of animal welfare.
"George faced many difficulties during those early years, particularly during World War II, but now, 75 years on, we are still here, stronger than ever."
Today the zoo covers 110 acres, welcomes more than 1.3 million visitors a year, supports conservation projects across the globe and has been named by Forbes as one of the best 15 zoos in the world.
Mr McKeown added: "None of what we have achieved in recent years would have been possible without George's initial tenaciousness - the zoo has seen some tough times but George's solid determination and steely resolve ultimately laid the foundations for success.
"He had a plan for a zoo without bars and so began a new design concept for zoos which is today mirrored all over the world."
The zoo has recently announced a £225m plan that will see it transformed into the largest conservation, animal and leisure attraction of its kind in Europe.
This will include a domed ecosystem which will be an African rainforest-themed sanctuary for a band of Gorillas, a large troop of chimpanzees, Okapi and a wide variety of tropical birds, amphibians, reptiles, fishes and invertebrates.
Planning permission is also being sought for a 90-bed hotel and a conservation college.