"In the past, if you'd stepped in this elevator by mistake, you faced being shot at the other end," is the first line of narration in this video. 

That's more than enough to catch our attention. 

Ten stories below Grand Central Terminal sits a giant "secret basement" that's housed nine rotary converters since 1913, machines charged with powering the entire MetroNorth rail system. 

Once World War II rolled around, the transport hub became integral to the war effort, but it gets more way more mysterious than that... 

You see, there was a German spy working in the facility; Hitler sent submarines and saboteurs; and well, watch the Science Channel video for the rest of this amazing story...

Check out Grand Central Terminal's Best Kept Secret Is Worth $20 Million Dollars. 

[via 6sqft]