DENVER — One mystery inside the Denver City and County Building has been solved. But two more remain.

For years, a vintage safe has made its home inside the Denver City Council offices. Before that, it resided in the Denver Sheriff’s Department that used to occupy the offices.

“Nobody’s got it open that we know of,” Denver City Council President Jolon Clark told FOX31, looking at the safe that’s in his office. “And so (it’s been) a mystery from my first day in office.”

When Clark was elected to the City Council in 2015, he’d began to bring his kids into the office when they were out of school.

Chloe, 11, and Logan, 13, soon became fascinated with the safe and tried cracking it.

“It’s a really big mystery because it’s been sitting here,” Chloe Clark said.

The two even watched safe-cracking videos on YouTube and recently started using a stethoscope to listen to the inner workings of the lock.

On Monday, the councilman was on the telephone in another room while the kids continued to tinker with the lock.

Chloe and Logan said they heard a click and the lock stopped moving.

Then they pulled the handle and no one could believe what happened next: the safe opened.

“When we got it open, we were really excited,” Logan Clark said, “Like, really excited.”

“I didn’t think in my wildest dreams they would get it open,” Councilman Clark said.

But what could be even more surprising than that was what they discovered inside.

Gold? Old photos? Important papers?

“It opened and there are two more safes,” Logan Clark said.

Chloe and Logan haven’t cracked the second safe and opened the other set of locked doors… yet.

Now they can’t wait for another day off school to get their hands on it.