Dirt Dauber.

A man awakes naked and confused in a isolated mountainous region, and soon encounters a strange local who offers to help him. The helpful stranger tells the man of local folklore that speaks of a murderous religious cult, a train tunnel cut deep into the mountain that leads to nowhere, and an insect-like fertility god that is said to dwell within it. The two men soon go underground in search of the truth, and find themselves in a stygian black temple of horror.