Publisher's blurb: The Cavern Passage group of Naked Geomorphs contains 19 tiles, each with two or more joined multi-position openings (CD, CSD, CSSD, etc.) and the remaining positions filled with rock (R). Sets A and B are completely interchangeable. I.e., tile C16B can be replaced with tile C16A, without changing the basic structure of your map. Set B has smoother, less complex outlines than set A.