Family Audio Tour Koornbrug
As you can see, many places here are named after goods that used to be traded on the Leiden market. Nearby, you'll find a Butter Market, a Fish Market, a Mustard Alley (yes, really!), and a Karnemelksbrug (Buttermilk Bridge).
Walk via the Koornbrug bridge through the Burgsteeg and turn left through the gate towards the Castle.
Click on the map in the lower right corner to see the route.