In the airport or at the airport?

https://thegrammarexchange.infopop.cc/topic/at-in-the-airport

RACHEL MODERATOR:
You are usually "at the airport."

The shops, etc. could be "at the airport" or "in the airport." "In the airport" actually refers to things inside of the airport terminal. "At the airport" describes a point where you are temporarily -- or at least supposed to be temporarily, but one never knows these days!

So you meet someone "at the airport." If, as in that old movie "Airplane," the plane actually crashes through the airport terminal building, it ends up in the airport.


RICHARD, MODERATOR (GUEST)

I explain to my students that, in this usage, at means the general location and in means a specifically enclosed place. Here are some examples to juxtapose the two:

He works at the airport.
He works in the control tower (at the airport.)

My classroom is in Building C.
I teach at Lipkey Hopkey Technical College.

I'm having a party at my house this Saturday evening.
When you arrive, please leave the food you're contributing in the kitchen.

And here's an interesting idiomatic usage:

(on the phone)
A: Hi, Neil.
B: Hi, Jan. Where are you?
A: I'm at the hospital?
B: Oh? What's wrong?
A: I'm visiting my aunt. She's having some tests done.

(on the phone)
A: Hi, Neil.
B: Hi, Jan. Where are you?
A: I'm in the hospital.
B: Oh? What's wrong?
A: I need an operation. They're going to take out my gall bladder.

As you can see, at the hospital simply identifies somebody's location in this case. We would normally use this phrase for a hospital employee, too: He works at the hospital.

The phrase in the hospital usually refers to patients. Ah, the wonders of English!