Photographer Robert Hackman has created a photo book that documents the many bunkers that were built in Albania between 1975 and 1989 amid fears of the Cold War.
Estimated to number up to 500,000, some bunkers are in states of dereliction or have been converted into cafes, homes, restaurants, swimming pools, barns, bridges and water tanks.
During the uncertain years of the Cold War, when nations prepared for the prospect of a devastating nuclear war, Albania's dictator Enver Hoxha convinced the country that the outside world wished to overthrow their communist state.
Rather than produce technological deterrents, bunkers were mass produced. Hackman's book, called Metamorphosis, shows the bunkers as they appear today.
Hackman says: "Concrete fabrication factories in every municipality began constructing bunkers 24 hours a day, every day of the year from 1976 until 1989.
"One labourer that I interviewed told me that the factory he worked in rotated in three shifts of eight hours each. Each shift made different parts so that no one person knew the exact constructional details of the bunkers they were building.
"Another, a field engineer responsible for erecting the bunkers, informed me that he worked 10 hours a day, every day for eight years.
"When asked if he ever questioned the perceived threat and the need for the bunkers, he replied that they were regularly given false air raid alarms to condition their thoughts."
"The majority of the Albanians view the bunkers as a hindrance and an obstacle, but rarely ever an eyesore.
"There are just so many that they have become accustomed to their presence, much the same as a Londoner with red telephone boxes or New Yorkers with yellow cabs.
"They have become a part of their lives woven into the fabric of their environment."
"A farmer showed me an infantry bunker with a small section of its side removed to make way for a path.
"What looked like a small amount of labour, had actually taken him and his brother three days to remove with a jackhammer.
"Higher up the hill was another bunker holding his TV antenna and housing his pigs."