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 C16A can be replaced with tile C16B, without changing the basic structure of your map. Set A has more complex outlines than Set B, with narrow protrusions and indentations.