From the back of the book:
"Build Your Own Dark Labyrinths
Your tabletop never looked better! With Dungeons & Dragons Miniatures and this pack of customizable grids, you can add a new dimension to your D&D adventures.
Easy to set up and infinitely expandable, this pack allows you to create the Underdark adventures you want to play. Pick up additional packs to create larger, more elaborate complexes!
This pack contains six durable, fully illustrated dungeon grids, featuring subterranean locales, lava pits, underground rivers, and other terrain elements that you can use to make great D&D encounters that enhance your roleplaying game experience.