Hidden Siberia

In the middle of the Siberian forests of Russia, lies an ancient site forgot on purpose by the Soviets who have hide this place for so many years. Stretching for many miles. Almost everyone who lives near this place, doesn't even know it exist. What have they been hiding for so long?
This documentary was recorded in 2019 and the sequel is called Return to Hidden Siberia. Which is also posted on my Youtube account by the same user name.