It’s on the underside of our cabinet in the house we recently bought, built in the ’70s. Any ideas what it could be?

We recently bought a charming house built in the 1970s, and while reorganizing the kitchen, we stumbled upon something intriguing. There’s a small, rectangular metal box attached to the underside of one of the upper cabinets. It’s painted the same color as the cabinet, making it almost blend in completely. There’s also a tiny keyhole on one side.
We’ve been scratching our heads trying to figure out what this could be. Maybe a hidden safe? A secret stash spot? Something related to the house’s retro design?
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If anyone has any ideas or has come across something similar, we’d love to hear from you! Your insights could help us unlock a piece of this home’s history.
Thanks in advance!