The Great Mist

If one travels far enough in any direction, they'll find The Great Mist. This wall of fog marks the end of the world, "where infinity ends" in the words of the merchants, who will go near anywhere. If one goes into the mist only a few hundred yards, they may find a small island or two with riches galore, but if they go in too far, they never return. Ships go missing routinely in this border, and nobody knows what lies beyond it. Sometimes, ships return from the mist, though almost always without the crew. When part of the crew does return, it's only ever one sailor, and they aren't in the right mind to talk about what lies beyond The Great Mist, seemingly driven insane by the horrors. The Great Mist is also responsible for otherworldly visitors, much like Ground 0 occasionally spits out humanoids, so does The Great Mist, though they know who they are and their goal is inevitably to get home. This is, however, far more rare that humanoids from spawn, which is already incredibly rare.