20 Ft Below: The Darkness Descending (2014) online

Below the streets of New York is a dark and dangerous world hidden in the shadows of abandoned subway tunnels and miles of forgotten infrastructure. When a young documentary filmmaker goes into these tunnels to uncover the unseen stories of the people living below our feet, she finds out that there is more to be afraid of than the dark. A mysterious figure, living beyond the reach of the law, has declared war on the outside world that threatens to tear apart the fragile underground society living in the tunnels and maybe even the city above it.