Publisher's blurb: The Cavern Basic and Tunnel Passage (small cavern) group of Naked Geomorphs contains 18 tiles, each with three openings, one of which is an unconnected two-position opening (CD) and the other two are a pair of connected tunnel openings (T). Sets A and B are completely interchangeable. I.e., tile M76B can be replaced with tile M76A, without changing the basic structure of your map. Set B has broad, unrestricted passages with just a few narrow blind branches.