Eight tight switchbacks drop beneath you here, the most photographed block of Lombard Street on the steep Russian Hill face in San Francisco. The block was originally straight, paved with cobblestones, and had a grade of 27 percent — too steep for most early automobiles to manage safely. In 1922, city engineer Clyde Healy redesigned the block with eight hairpin turns to reduce the effective grade to approximately 16 percent.
The switchbacks were planted with hydrangeas by a neighbor named Harriet Pullman, who thought the bare concrete needed color; the plantings have been maintained by the city and residents ever since. The engineering compromise that created the crooked block has become the block's reason for existing in the popular imagination, drawing more than two million visitors a year who wait in summer traffic jams to drive down at five miles per hour. The residents of the block have fought for years to restrict tourist access.
Less famous but arguably more crooked is Vertiginous Vermont Street in Potrero Hill, which has a tighter curve radius, but Lombard got there first with better marketing. At the bottom of the switchbacks, Coit Tower sits framed in the gap between the buildings.