A 529-foot stretch of Baldwin Street in Dunedin, New Zealand has a gradient of 1 to 3.41. There are roads elsewhere in the world that are steeper, but no one is crazy enough to live on them.
But the Kiwis do not take such challenges lying down. They prefer leaning over, which is why they get to claim this Guinness World Record title.
How did this happen? City planners in London considered that a grid plan is the best way for a city to develop, so they designed it that way for Dunedin. They did not give much regard for the local topography. You can see more photos of this amazing place at Twisted Sifter.