I have a very soft spot in my heart for TSR's World of Greyhawk—if not the campaign setting, definitely the map. It's one of my favorites. That may be because it was my first exposure to a D&D world setting. But this, this I never noticed. The lake of unknown depths is very obviously Lake Superior. Which is very cool. But being a Michigan native, I feel like I should have noticed that at some point in the last 30 years. Fortunately, the internet stepped in and pointed it out to me.