San Francisco as a place of great Evil. Presence you could feel, physical: something that disliked humans.
One day you found it, while riding in the back of a friend's car inbound on California Street. In the fog the spires of gray buildings, and your tension rising block by block, not knowing why, fear, the instinct to fly. Gothic. Grace Cathedral. Somebody lives there. You can feel it pressing on your heart. As you pass it immediately fades, falling block by block, still not knowing why, but now certain you'll never go there alone.
You avoided the place for years until one day it was gone. Vanished. Only after that were you were able to walk the lovely labyrinth there in peace.