Game Tiles Narrow Dungeon Passage Pack is made of "Dwarvenite" and expands the Games Tiles Base Set. It was offered as an add-on pack during the Cavern Kickstarter. The pack comes in both painted and unpainted versions.
The Game Tiles Narrow Dungeon Passage Pack comes complete with these 20 pieces:
(2) Conversion, Wide to Narrow
(6) Passage, Dungeon, 45 Degree
(12) Passage, Dungeon, Narrow