The switchbacks were added in 1922, when property owner Carl Henry proposed the serpentine design to reduce the grade from 27 percent to a more manageable slope. Before the turns, the street was a straight, terrifyingly steep descent that horses and early automobiles could barely navigate. The eight turns, each banked and separated by raised flower beds, transformed an engineering liability into an urban landmark. The brick-paved roadway was designed for safety, not spectacle -- but spectacle is what it became.

Lombard Street's fame has created a paradox: the more people visit, the worse the experience becomes. On peak days, cars wait 30 minutes or more to drive the one-block descent. Tour buses idle on the cross streets. Pedestrians crowd the sidewalk stairs. Residents of the street have repeatedly sought relief from the city, proposing tolls, reservation systems, and outright closure to tourist traffic. The street appears in virtually every San Francisco tourist guide, every film set in the city, and every social media feed of anyone who has visited.

Lombard Street extends far beyond its famous block, running east-west across the northern part of the city from the Presidio to the Embarcadero. Most of it is an unremarkable urban street. But between Hyde and Leavenworth, it becomes something else -- a piece of civil engineering that accidentally created one of America's most recognizable landscapes. The hydrangeas bloom in pink, blue, and purple. The brick pavement is worn smooth. And the cars keep coming, one hairpin turn at a time.