East German authorities began patrolling the inner-German border in 1952. Until then it had been relatively easy to pass between the two. They sealed off West Berlin in 1961. Here, soldiers keep people from crossing as the Berlin Wall is built.

In 1961, communist East Germany was having trouble keeping its young, educated population from emigrating to the West. The Berlin Wall was erected almost to completion in a single night, without warning, on August 13.

This famous photo from September 1961 shows a woman trying to escape East Berlin through an apartment block where one side of the building faced the West. Some men try to pull her back inside while others wait underneath, hoping to aid in her escape.

Amidst mounting internal and international pressure, a mistaken announcement by an East German official on November 9, 1989 led to the wall being opened. Germans on both sides of the border celebrated for days. New openings were made in the wall, like here at Potsdamer Platz two days later.

Today, some parts of the Berlin Wall still stand as a memorial to hard-won freedoms. The famous East Side Gallery allows different artists from around the world to add murals to the part of the wall that remains on Mühlenstrasse in Friedrichshain-Kreuzberg.

Politicians for the state government of Berlin lay flowers along the site of the Berlin Wall on Bernauer Strasse, 56 years to the day after it was constructed. At least 140 people were shot dead by East German border guards at the wall from 1961 to 1989.

The "BT11" in Kühlungsborn is a former East German border watch tower. From 1973 to 1989, Costal Brigade soldiers used to be on the lookout for escapees. Those looking to flee the communist country would try to reach the coast of Schleswig-Holstein or a passing ship from here. Today, the tower is a listed monument and one of the last surviving of some 70 such lookouts along the coast.

The former death strip along the East-West border has proven to be a stroke of luck for nature, even 26 years after the Iron Curtain was opened. The Green Belt between the Elbe Altmark marshes and the Wendland seems to magically attract migratory birds. Large flocks of geese, swans, ducks, and cranes stop and rest here every autumn on their way south.

Ninety-five of the altogether 1,091 kilometers of the Elbe River used to be part of the exclusion area of the inner German border. Subsequently it has remained mostly untouched - like here near the village of Lenzen - making it one of the few surviving natural waterways. With its changing water levels, it forms the wetlands that make up the UNESCO-listed Middle Elbe Biosphere Reserve.

The main function of the East German blockade was to prevent citizens from escaping. This makes it different from other border posts, where guards would face outwards to defend against threats from the outside. In Hötersleben you can see some original parts of the border posts, including watch towers and anti-vehicle obstacles.

This northern part of the Harz region is characterized by gently rolling hills from which the Grosse Fallstein emerges as a special vantage point. The 70-kilometer cycling tour along the Green Belt from Hornburg to Ilsenburg is particularly attractive. It leads past orchards, fields and chestnut-lined roads, and through untouched nature and the remains of former border posts.

Located on the former inner German border, the peak known as the Brocken was inaccessible to citizens of both West and East Germany during the Cold War and subsequently became a symbol of the country's division. With the fall of the Berlin Wall, the Brocken again became a center of interest and has drawn countless visitors since reunification.

This symbolic memorial to mark reunification of both German states in Sorge close to Wenigerode is a circular area into which dead wood has been placed on a diameter of 70 meters. Artist Herman Prigann said that as this tree rampart slowly becomes overgrown with plants, it will encourage reflections on decay and growth.

The border post is all that remains of the former inner German frontier on the Warteberg by Nordhausen. In the shadow of the Iron Curtain along the former patrol path, habitats and refuges for rare animal and plant species have developed. Endangered species like orchids, black storks and large saw-tailed bush crickets have found safe retreats.

The Borderland Museum Eichsfeld has been situated at the former Duderstadt/Worbis border crossing since 1995. Until 1989 nearly six million travelers used the border crossing between the villages of Gerblingerode in the West and Teistungen in the East. The history of German division is displayed over some 1,000 square meters. This includes former border security posts and frontier barriers.

During the Cold War, the Staufhain mountain and the village of the same name were located in an area that could only be accessed by border soldiers. The ruin was turned into an observation tower and listening post. The surrounding forest grew unhindered and soon it became a mountain of dreams. On December 3, 1989, the mountain was opened to visitors for the first time.

Our tour of the Green Belt ends in Mödlareuth, a village of 50 people. American soldiers used to call it "Little Berlin," because, like its big brother Berlin, it became symbolic of Germany's division. Like in the German capital, the Thuringian-Bavarian Mödlareuth was divided until 1989 by a concrete wall that was 700 meters (765 yards) long and 3.4 meters thick.

The Iron Curtain divided Germany and Europe for nearly four decades. Walls, barbed wire and watch towers separated families and friends. What was once separated is now united by nature. The Green Belt is the first pan-German nature preserve.