Its Tremulous Lair Bears Beings Betwixt

From publisher blurb: A glistening tunnel network. Its glutinous walls and troves of spoil line a fecund darkness in which delvers are made anew. Condensed to one page for slipping in among other materials, this sandbox-oriented content is intended as an easily absorbed framework for improvisation to be adapted by the user as preferred for a wider setting and specific system. It presents core ideas and key numbers to fall back on, with general approaches that can be applied in other situations. The content covers map generation on the fly for an abstracted tunnel network as well as suggestions for aspects of the locality, including mouths, occupants, transformed matter, gelyp grafts and development. The scrabblers could be detailed with items from Character: Odds & Ends Found on the Olde Worlde Adventurer, while the tunnel network could be simplified or extended using one or more of the maps in the Location, Landscape & World bundle, most obviously The Vermian Maze.