They were mostly dirt or stone lanes with vegetation on either side, and already piled with horse, goat and sheep crap. The more civilized folks who lived in rowhouses piled the poop all together at the corner, high. But day to day, out the window:
The wealthy had servants to clean out their castle toilets:
Thats gotta give you one hell of a backdraft if the wind isnt right. Better check the weather before. I bet them castle walls are cold on gentile skin.