Michal Wilczewski tweeted a picture of a door drawn with chalk with "Hogwarts" written above it at the Damen Blue Line stop and asked Rowling for more information.
Rowling responded that, "It's for exchange students from Ilvermorny. Duh."
After getting a response from the famous author, Wilczewski callied it, "The most magical day of my life!"
And the CTA now says that they are updating their maps.