Death From Below: Or How I Learned to Love the Tentacle

From the introduction: The local mine has become desolated by a recent disturbance unearthed by the workers within the chambers of the mountain. A tentacle horror has taken residence and is now corrupting the very mountain into its own living lair. It has thrust appendages into the mine and taken over the area as it devours any energy (and people) it can obtain. Recent expeditions into the mine have reported insect like vermin working symbiotically along side the beast. Some have felt psychic screams for help deep within the tunnels. The only adventurers to return have later died from hatching spawn, corrupting their very minds, compelling them to infect others. Many destroy themselves before the madness corrupts them and the plague uses their body as a new vessel.