For all Berlin’s attractions, it is a small, wooden shack that tops the must-see lists of many tourists here.

The former guard house stands behind a row of sandbags at a busy intersection in the heart of the city’s downtown, beneath a sign announcing “U.S. Army Checkpoint.” The world knows the spot better as Checkpoint Charlie.

It was at this crossing, during the Berlin Crisis of 1961, that Soviet and American tanks stood muzzle to muzzle in a standoff that threatened to plunge humanity into yet another war, this one to be fought with nuclear weapons. After six tense days, the two sides backed off without firing a shot. But the site remained ground zero of the Cold War division that split the world into opposing blocs.

“There is no equivalent anywhere, where tanks stood off and the world worried we were on the brink of World War III,” said Hope M. Harrison, a professor of history at George Washington University, who has studied Cold War Berlin and the city’s development since the Berlin Wall came down. “That is what is so unique about Checkpoint Charlie.”