Why kick the door down when you can get in behind a cleaner.
I was at a so called secure site. Visitors badges were paper so could not get through badge locked doors.
Someone was having deliveries and so the outside door was open - in we went and could roam around the building.
We got to the ops room, which was being cleaned, the usual way. Use a bin to block the door open while the room was being cleaned. The cleaners were not allowed to use a power socket in the ops room, and so needed to get the cable for the vacuum cleaner into the room.
In we went, sat down and started writing our presentation.
Half hour later in walked the IT manager who asked how we got in!
This was a different site to a colleague in the US who was at a secret secure site. He was permanently escorted by a marine with an automatic rifle. When he went to the bathroom, the cubicle had no door, and the marine watched him do his business.