Almost twenty years ago, a lady walked into my former employer, from right off the street, to ask that they unsubscribe her from the mailing list. She was in town on vacation and realized their offices were there, and just thought it'd be nice to get that dealt with in person. Especially because her attempts to unsubscribe electronically had repeatedly failed.

Almost fifteen years ago, another of my former employers had an angry customer storm into their office and start shouting at the front desk associate. Soon after they relocated, and hired a full-time armed security guard to process all visitors straight from the elevator lobby. Any further, and you'd need to present photo ID and maybe sign an NDA before he'd buzz you in.