It's interesting the way a city shows its age. Take for example, these stalactites dripping through a crack in a part of the CTA's rail system. You've probably seen these all over town. There used to be some epic ones at the Randolph & Wabash station and in the transfer tunnel between the red and blue lines. I bet there's still some in the Blue Line station at Grand.
While stalactites take hundreds of years to form in caves, the CTA seems to be able to grow them in a matter of just decades.