I don't suggest doing this.

Drop ins are NOT welcome at most places I know. People need to be met at the door, signed in, escorted, etc...on top of that many departments like to keep things as private as possible.

I would highly suggest calling first and making an appointment or an inquiry about hiring. Even if you get dumped into voicemail, just ask if there is a good time to stop by, say hi, and leave a resume for the future. Often as simple as "Im at the airport today and would like to drop off a resume if you have a free minute" may get you a call back.

"Dropping in" is often considered rude and certainly not worth shooting yourself in the foot when a courtesy call would work just fine.

Good Luck!