Publisher's blurb: The Cavern-Tunnel Passage (large cavern) group of Naked Geomorphs contains 18 tiles, each with one three-or-more position opening (CSD, CSSD, etc.) and a connected tunnel opening (T), with the remaining positions filled with rock (R). Sets A and B are completely interchangeable. I.e., tile M13B can be replaced with tile M13A, without changing the basic structure of your map. Set B has broad passages without narrow restrictions.