Penumbra is real - possible inspirations?

[Saty]

There was a story of Lizard men(Reptilian beings) abducting people in one of the underground cavern/mine system.People would enter them and never return.There are these reptile/insectoid being living deep beneath the earth and those aren't just legends.I honestly would never enter them, hell risking my life in a dark place where nobody could here me scream.No thanks.
Look up the movie called "DESCENT". There is a lot of truth in that movie.They went too deep and BAM!
Lost tapes did 2-3 episodes of these Lizard walking creatures.