There are a few streets in my area that hit 25% - 30% for short periods,
but the steepest climb of any significant length that I've done is the
Mt Washington Auto Road.
It averages 12% for 7.4 miles, never drops below 6%-8%, has extended sections at 16%-18% and hits 22% at the end.
It gains 4,678 feet in 7.4 miles.
There is a
race every year in August.
Weather can be anything from warm & sunny to windy, rainy or cold with hail or snow.
It is brutal, unforgiving and incredibly rewarding at the end.