BUSCAP is correct... I'd make sure you have your ID CLEARLY visible and kindly ask a UAL mainline crewmember if they'd mind showing you to it, door code, etc....

The C-con elevator next to the escalator that goes down to the underground neon moving walkway would be a great place to hover around to get the skinny from a Mainliner... or a Regional dude, but I'm not about to give any more info than that.