While wandering through the Mojave, looking for the Strip, you find a trading post and a bunker. You decide "Huh why not enter the bunker?"...

You tried to open the bunker, but to nothing. Oh, silly you. There seemed to be a control panel outside. You plugged in your pip-boy to the port, pressed to open the bunker, and it slid open. Huh, interesting..this wasn't a vault.

You immediately saw a girl rush out and speak to you..

Veronica: "Who the hell are you, and most importantly how the fuck did you open that door?"