Publisher's blurb: The Tunnel Passage group of Naked Geomorphs contains 12 tiles, each with a pair of connected tunnel entrances (T), and rock (R) at the remaining four positions. There are actually nine different interconnection patterns; this group contains two tiles for each pattern where the tunnel positions are adjacent, because those are so useful as edge and corner tiles. Sets A and B are completely interchangeable. I.e., tile T77A can be replaced with tile T77B, without changing the basic structure of your map. Set B has broader tunnels than set A, with no one-hex-wide constrictions in the main passage and occasional small offshoots.