Zoo Hill - named after the small zoo at the bottom - is arguably the toughest climb in the Seattle area. Ascending 1200 feet over 2.5 miles, it has an average grade of about 10%, with common gradients in 15% and some sections approaching 20%. This is not a climb to be approached lightly.
Or, as one rider noted, "Zoo Hill is the puke-inducing lactate-producing gasp-fest that I avoid unless taunted"
If you don't want to do the whole climb, you can do the short version to the stop sign, which is 12000' with 1000' of vertical.
Descend by continuing straight at the stop sign, down to Lakemont Blvd.