Have you heard of the Bermuda Triangle of the Great Lakes? Numerous things have gone missing in this area, including many ships, a captain, and a plane. There has also been several accounts of strange lights and other happenings. Here's my interpretation of the mysterious zone.
"Here be dragons" is a remenant of old maps where catographers would put the phrase in unknown areas with potential danger.
There is also a nod to the mysterious Stonehenge found underwater in the scribbles at the bottom