Quick answer
Lombard Street's famous block sits on Russian Hill between Hyde and Leavenworth. Its eight switchbacks were built in 1922 to make a 27 percent grade driveable, cutting it to about 16 percent. Property owner Carl Henry proposed the fix and city engineer Clyde Healy designed it. Vermont Street on Potrero Hill is arguably crookeder.
Full transcript
The Hill Was the Problem
The block of Lombard Street between Hyde and Leavenworth was originally straight, cobbled, and pitched at a twenty-seven percent grade. That is steep enough that the cars of the nineteen twenties simply could not climb it, and steep enough that walking down it in the wet was genuinely dangerous. In 1922 a property owner on the block named Carl Henry suggested a fix: instead of fighting the hill, wind the road across it. The city engineer, Clyde Healy, took the idea and built it. Eight sharp switchbacks, cut into a single block, dropping the effective grade from twenty-seven percent to about sixteen. It was not designed to be charming. It was designed so that the residents could get home.
The Title Is Wrong
You will see this street described everywhere as the crookedest street in the world. It is not, and the counterexample is a fifteen minute drive away. Vermont Street, in the Potrero Hill neighborhood, has seven turns to Lombard's eight, and it sits on the steeper hill of the two. It has no hedges, no hydrangeas, no queue of cars, and almost no visitors. Lombard won the title because it is beautiful and because it sits between two cable car lines, which is a different competition entirely.
How to Actually Do It
If you drive it, you will spend twenty minutes in a queue on Hyde Street to spend two minutes at walking speed looking at the bumper in front of you. There is a better way. Park elsewhere, or take the Powell-Hyde cable car and get off at the top. Walk down the brick staircases that run along both sides of the switchbacks. You will get the gardens, the view down to Coit Tower and the bay, and the photographs, without the traffic. The homes on either side are private residences whose owners have lived with this for a century, so keep to the steps and keep the noise down. Start down the steps early, before the tour buses claim the block.