Weakness of Rock

Publisher's blurb: Something stirs in the Hulburg mines. It would be nice to know what, but it would be nicer if it would stop collapsing parts of the mines and leaving catatonic miners. This could be the end of Hulburg’s windfall unless someone finds a way to stop it. Part 1 of the Obsidian Stone trilogy. A four-hour adventure for 11th - 16th level characters