Here is a map border recently completed for Goodman Games. I redacted the text and maps (since Goodman hasn’t published this yet — no spoilers!) but we can see a weird globule creature attacking someone seeking refuge in a palm tree and all kinds of corrupted weirdness around the edges. The maps and text fit into all of the white space.
I find this kind of stuff really fun to do — perhaps because I grew up with a lot of books about medieval art and I always loved the perverse and whimsical little things those monks drew in the margins.