Action News was inside on a day that marks the beginning of the end for the Plutonium Finishing Plant (PFP).
It used to have layers of security, a check point outside, then metal detectors and X-rays inside. There are airlocked doors to keep contamination out and thick cement doors to get to the plutonium vault.
All the security and secrecy ended last month, when the last bit of plutonium was shipped off.
This is where some of the most hazardous material on Earth was stored, inside the vaults.
Two-thirds of the plutonium used in the country's nuclear weapons program was produced at PFP. Then, after the Cold War they stopped.
Leaving nearly 20 tons of plutonium to stabilize, package and store. Now it's all gone and workers can finally talk about the work they've been doing here.
"This was national security information so you didn't talk about it at home you just kept it to small groups you worked with," said Glenn Chapman.
"You don't talk about it at home, so yeah it's kind of weird. But it's a chance for people to actually see the work done and how safe it is," said Mike Bowles.
And there's still work left to be done. The feds put a deadline for demolition by 2016. But they are ahead of schedule and could be done three years early.
"It's bittersweet but it has to be done and be done right for the nation and the state," said Richard Wilbanks.
The reason this was built is now the same reason it will be destroyed: love of country.