They're remnants of the NW project, or New World project. This was from a very long time ago. Not much sense in going into detail since most people here won't realize the things I'd need to mention to have anything make sense. Anyways they're from like 2000, and it was a failed project overall for Graal(it was worked on by Stefan, though), but brought many new features to Graal in its failure. NW level format, ganis, NPC server are just a few things it introduced to Graal.
Anyways, cliffs came from that tileset.