There is an art to getting into places, and it isn’t stealth or smooth-talking. It’s being unquestionable.
The best camouflage you can ask for is other people’s general indifference. The more people there are, the more indifference they tend to have. If you want to get into a building that you technically shouldn’t be in, you just have to look at the kind of people that walk in unhindered.
People with reflective vests, clipboards, ladders, or tools generally walk in anywhere. People also don’t tend to question people carrying pizza boxes. If you’re carrying a bouquet of flowers or a heavy potted plant, that’s usually good too. Especially if you look vaguely confused and/or bored.
Don’t try to come up with a story. Act mildly frustrated. If someone asks where you’re trying to go, just say, “Dude, I have no idea.” Nine times out of ten, the person will suggest a valid reason you might be there! Then just say, “You know what, probably? It’s been a day. Which way is that?”
Don’t be trouble, and trouble tends to avoid you.
(Worth noting: Use these skills only for good, people!)
The Opportunity Machine 