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MASSWEILER, Germany — Deep in the forests of southwestern Germany, three tigers rescued from private homes have moved into their luxurious new residence — a former U.S. Army installation.

Animal welfare charity Tierart — "Animal Species” — recently opened a 34-acre state-of-the-art big-cat sanctuary, equipped with swimming pools, wooden "chill-out lounges" and rubber-ball entertainment for the stressed-out animals. The facility in Massweiler, near the French border, is believed to be the first of its kind in the country.

A former maintenance shed for military vehicles was renovated and turned into an indoor compound for the tigers. Their 16,000-square-foot outdoor enclosures are partly built above bunkers originally installed by the Nazis and later used by the U.S. army signal corps until they were vacated as part of the American military’s drawdown in Europe.

Two-year-old tiger Cara at her new compound in Massweiler, Germany. Andy Eckardt / NBC News

Two-year old Cara was found cooling off in her private pool at the sanctuary one recent afternoon. She was rescued from a farm in Naples, Italy, where she was kept confined in a windowless 64-square-foot shed.

Now Cara is a next-door neighbor to 14-month-old tiger siblings Bela and Shahrukh, who spend their days resting in the shade or watching a nearby herd of goats. The siblings were given to an animal welfare organization when their owner was unable to afford a necessary larger enclosure.

“The problem is that naturally, we humans are still on the menu of these animals"

Tigers can live for as long as 26 years and eat up to 11 pounds of meat a day.

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“For many, it is not exciting enough to hold dogs, cats or mice as pets these days,” Joerg Bruno Grabbert, the project manager for big cats at the sanctuary, told NBC News. “There is a downright boom in Germany to keep exotic animals,” added Grabbert, who lives in an apartment above the new tiger boxes.

Experts fear a growing demand for similar facilities “as approximately 150 big cats, all lions and tigers” are being kept in German circuses alone, according to James Brueckner, head of wildlife and nature conservation at Germany’s non-profit Animal Welfare Federation.

Animal charity Vier Pfoten — "Four Paws" — financed the project from donations and says the sanctuary cost more than $1.2 million dollars and took several years to create.

Vier Pfoten says it knows of 19 big cats being held by private owners and warns of the dangers. “The problem is that naturally, we humans are still on the menu of these animals, even if they grow up in captivity,” Martina Stephany, the charity’s Head of Programs told NBC News.

Back in 2009, three Bengal tigers attacked their animal trainer at a so-called "dinner circus" show in Hamburg. One of the most notorious tiger attacks occurred when Roy Horn, of former Las Vegas magic act "Siegfried and Roy," was bit in the neck during a live performance in 2003.

Security was one of the main reasons why Italian authorities seized two-year-old Cara from the private farmhouse.

Two-year-old Cara was previously kept in a cramped shed in Italy. Andy Eckardt / NBC News

“But it has become very difficult to confiscate big animals because there are simply too few sanctuaries across Europe,” Brueckner said. Most German zoos will not accept animals with an unknown genetic background because “to them, they are useless for breeding,” he said.

Animal rights organizations complain that laws surrounding the keeping of large animals is “too weak” in many European countries, including France, Italy and Germany.

“There is no political will to implement stricter laws,” said Brueckner. “It took nearly 20 years to increase the size of the enclosures for big cats from [430 square feet] to [2,100 square feet] in the official German regulations.”

Welfare organizations in Germany favor ex-military installations because they offer open terrain and good infrastructure.

Katrin Umlauf runs an animal sanctuary in the northern German city of Kappeln on a site purchased from the German military in 1995. The 32-acre facility has several former ammunition bunkers, which have been turned into winter quarters for bats or have been equipped with windows and doors to house abandoned horses, goats and pigs.

The Massweiler sanctuary was particularly attractive because it included a water well, offered buildings that could be redesigned for the big cats and had a secure outer fence. It can hold up to six big cats, but the vacant slots are already reserved.

"In the next four weeks, we will be receiving a tiger in need from a European circus,” Roswitha Bour, head of the Massweiler sanctuary, said. “And we are in negotiations with authorities about two additional circus tigers,” she added.