The Ghost Sea

Beyond the map border, starting at around X: -5800, lies The Ghost Sea. It is the first area a player meets outside the border, and the wiki presumes that going farther leads to The Void Ocean. It has the same structure as the Ocean, only without water, and the wiki says that was never an intentional creation.

It now counts as removed: an invisible barrier at X: -5690 blocks the way, though the wiki leaves open that there may be a hole in it somewhere. The Ghost Sea still counts toward bestiary completion.