Watch Series: Secrets of the Underground Released in (2017) - Season 1 produced by USA, The TV Series categorized in Reality-TV, Documentary, and content rating TV-PG with duration 60 min broadcasted as these networks Science, Science Channel, Streamed at Putlocker A search for an underground escape route said to have been used by Al Capone. Also: who or what built earthen mounds in Washington state. - Season 1