This is one of those weird Chicago things that you learn about on the Chicago Architecture Boat Tour (go do that if you haven't, by the way) or you learn about from your friend that went on that tour. Or, you learn about it from a mediocre website made by some dude that posts on TikTok (me). The mural (if it can be called that) is massive and sits on the side of a skyscraper along the Chicago River. On the mural is a map of the Chicago River, with a big red pin showing your/its current location. Now that you know about it, go tell your friends about it so you sound cultured and smart.