The Rhode Island State House.
The Rhode Island State House. Max Binder/CC BY-SA 3.0

A construction crew renovating basement offices in the Rhode Island State House was peeling back 1970s paneling from the walls when they came across a giant, black steel door, the Providence Journal reports.

The door looks to be connected to some sort of vault. It’s secured with an old combination lock—but no one knows the code. The only clue to the vault’s purpose or possible contents is what is written on the door: “State Returning Board.”

This board was created in 1901 to oversee vote counts, and it became the Board of Vote Tabulation in 1935. It’s unclear how long the vault has been locked and unused. Perhaps it was covered up in the 1970s because no one knew how to unlock it then, either.

For now, there are no plans to force the vault open. That would be expensive, and in state government anything that costs as much as taking a heavy, secure door off its hinges needs special approval.