(CNN)Editor's Note: This post was originally published in 2013.
Kai Wiedenhöfer photographed the fall of the Berlin Wall in 1989. He says he was deeply moved by the historic event, calling it the most positive political experience of his life.
It left him, and many others, optimistic about the future. He thought he had seen the end of walls like the one that divided his hometown for 28 years.
"This idea that we had -- that we would have a free world -- that proved to be wrong," he said. "We had a big renaissance of walls."
From 2003 to 2006, Wiedenhöfer documented the construction of the controversial barrier between Israel and the West Bank. Then he expanded his focus to photograph other boundaries set up in response to global conflicts.
Preferring to travel without a security escort, it was important for him to plan ahead and work quickly. He tried to spend less than 20 minutes taking pictures each time he went out.
"You cannot stay long in places," Wiedenhöfer said, noting that there wasn't usually much activity along the walls. "Before people who can do me any harm get there, I'm gone."
When he visited Northern Ireland in 2008, he thought the so-called "peace lines" dividing Catholic and Protestant neighborhoods might start to come down. Instead new walls were constructed and old ones were reinforced.
Over the last seven years, Wiedenhöfer has also been to the fence along the U.S.-Mexico border, the demilitarized zone separating North and South Korea, and a wall in Baghdad built by the U.S. Army. In all, he made 21 trips to eight different walls.
The resulting photographs will soon be published as a series of diptychs in his latest book, "Confrontier." While acknowledging the unique circumstances of each wall, Wiedenhöfer said he paired images together to emphasize their similarities.
Beyond the book, he had more ambitious plans.
His long-term goal was realized last week when he launched an exhibit of his panoramic images on the longest surviving stretch of the Berlin Wall. Each picture is displayed at 3-meters tall by 9-meters wide, or roughly 10 by 30 feet.
Wiedenhöfer negotiated with the city for five years to get the necessary permits and raised money on the crowdfunding platform Kickstarter to cover the expenses.
"Walls are no solution for today's major political problems, and I think the Berlin Wall is the best proof of that," he said at the "Wall on Wall" opening.
These days it's hard for him to imagine a world without walls. But he wants to remind people what Berlin demonstrators chanted in 1989: "Die Mauer muss weg -- the wall has to go."