An abandoned system of caves was once the meeting place of a secret society that worshiped Satan and performed black magic. New discoveries at this mysterious site reveal what really happened here and why a Founding Father was a frequent guest.

The Soviet Union built countless engineering marvels beyond the Iron Curtain, but today, these mysterious places are abandoned; experts use cutting-edge tech to reveal the secrets of how they were built and why they were abandoned. The segments of this special come from various episodes.