SEOUL (Reuters) - As a united Germany marks the 20th anniversary of the Berlin Wall’s fall on Monday, about 1 million soldiers face off across the Cold War’s last great divide -- the Demilitarised Zone (DMZ) separating the two Koreas.

Tourists look at South Korean flags and reunification banners hung on a barbed wire fence, on Freedom Bridge at Imjingak pavilion near the Demilitarized Zone (DMZ) separating the two Koreas in Paju, about 52 km (32 miles) north of Seoul, November 9, 2009. As a united Germany marks the 20th anniversary of the Berlin Wall's fall on Monday, about 1 million soldiers face off across the Cold War's last great divide -- the DMZ separating the two Koreas. REUTERS/Jo Yong-Hak

The 4-km (2.5-mile) wide no man’s land, established under the ceasefire that ended the 1950-53 Korean War, runs 245 km (150 miles). It divides the peninsula with razor-wire fences, minefields and one of the heaviest collection of armaments on earth.

The Berlin Wall anniversary has sparked a longing in South Korea for unity but also worries about the enormous costs involved if the DMZ was dismantled and North and South Korea were united.

“The economic gap between the two Koreas is far wider than that of the two Germanys before reunification,” the Dong-A Ilbo newspaper said in an editorial.

North Korea is an economic backwater, with annual GDP of $17 billion in 2008 -- two percent the size of the South’s economy.

By some estimates it would cost more than $1 trillion for South Korea to absorb the North, the only real scenario in the event of reunification.

That would wreak havoc on South Korea’s economy, with a state-funded research agency saying it would raise the tax bill for South Koreans by the equivalent of two percentage points annually for 60 years.

Aside from the huge costs, there has been virtually no contact between the two Koreas for decades, which have cut off almost all phone links and mail and did not have a formal meeting for about 20 years after the war.

East Germans by comparison were able to see the outside world through West German TV and the two countries had far more exchanges of people.

Recent polls show more than 60 percent of South Koreans want unification, but they would prefer it happen later rather than sooner because of the cost.

About 70 percent of respondents see the North as a threat and few think it will give up its nuclear weapons any time soon.

FACTORY PARK AND MOUNTAIN RESORT

What little cooperation there has been in recent years between the Koreas has been confined to a mountain resort and a joint factory park located just north of the DMZ.

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The projects, complete with new road and rail links, were built by the South with the help of an affiliate of the Hyundai conglomerate and have seen their fortunes ebb and flow as ties between the two states have gone from warm to frigid.

The DMZ is one of the most popular tourist sites in South Korea, attracting more than 600,000 visitors a year who see tank traps as they head toward the border and tunnels the North built under the zone decades ago to support an invasion.

The highlight of most tours is the Panmunjom truce village that hosted the armistice talks and which sits within the DMZ. It is now home to uneasy staring matches between soldiers from the two Koreas as well as U.S. forces in the South.

The actual border is called the Military Demarcation Line and is only an ankle-high strip of concrete in Panmunjom. In most of the DMZ, it is marked only by 1,290 yellow signs less than one square meter in size.

If the DMZ ever comes down, South Korea wants to set up a nature preserve in the long strip, which has become a haven for wildlife including endangered species of birds, thousands of types of plants and 70 different mammals.