It's easy to get mad about this, everyone would prefer the fancy ceiling. But a lot of old plaster work like this was cheaply and hastily made, a lot of what survives is in bad shape. There may have been good reason to add a barrier between the plaster and the people below. This may even have been the best choice for preserving the plaster until an owner with greater resources could restore it.

This picture invites you to tell yourself a story about what happened, but it doesn't give you enough information to know what happened.

Always makes me sad to see nice plaster work hidden or removed.

Is the ceiling giving birth to an alien?

Potentially a ceiling cover which contains asbestos, so they cover it up rather that deal with it. It's not necessarily hundreds of years old.

This is actually a lucky incident. By covering it, the plaster actually survived.

From the thumbnail I thought this was some joke where someone found an upside down alien artifact or something.

I’d be pissed if they had this nice eldrich ceiling in my office and covered it up with standard municipal paneling

The lengths bean counters will go to save a few bucks.

They reduced their air conditioning costs. The picture maybe even omit where they ran ducting that was hidden by the drop ceiling

Also, the fluorescent lights are much cheaper to operate than incandescents

But it is a mortal sin to drill a hole on that plaster to hang a crappy ceiling.

That is genuinely infuriating.

At first I thought this was bathroom tile with printed designs on it, and I was so confused

Portal on LV-246.

Save Bandit!

Fancy ceiling or angry contractor?

"Bought the place from a feller used to have some kinda rituals in here. We put in that ceiling cuz the new tenants complained about whispery voices."

Secret assassin tomb!

Fear of the plaster dropping and causing a lawsuits is my guess.

Corporations are an invasive species.

There's a prison described like this in the far future series Book of the New Sun