Matthew and Maria Emanuel, from Staten Island, New York, USA, made the astonishing discovery while having a new tree planted.
They spotted the box, submerged in the dirt – which turned out to be a safe filled with more than they could have ever expected.
When they broke inside, they found wads of cash, bags stuffed with diamonds and gold rings.
"You dream as a kid that you find buried treasure and it happened, it was unbelievable," Matthew told the Staten Island Advance.
AMAZING: The contents surprised everyone
“We found buried treasure”
"I didn't know it was a safe, I just thought it was some kind of electrical box.
“I thought, We found buried treasure!' We were freaked out – its something you cant make up."
But alongside the finding, they also uncovered a Brooklyn address written on a piece of paper – which they soon linked to one of their neighbours.
Matthew added: “We realised it must have been them, so Monday morning, I walked on over to their house.
"I knocked on the door and I asked them if they were ever robbed, and they said they were.
"She was shaking."
New York Police later revealed a burglary was reported at the address in 2011 and a safe of the same description was taken.
The neighbours, who did not want to be named, admitting they were "surprised and grateful".
The couple have now placed a white statue of an elephant in the spot where the safe once sat, to serve as a reminder of the astonishing discovery.
They have not received ant kind of reward yet but admitted they did not do it for that reason.