there is an elevator by the lobby. I don't remember which floor, but you can only get out to Mozen bistro floor or Mandarin bar floor from the elevator.
Once you step out of the elevator, there is another lobby/front desk. That confuses people I think.
Hope this help. I am more of a visual person. bad at giving directions verbally.

 

When you walk into the lobby, the elevators are on your right. If I recall, the elevator only has like one or two buttons. There's also a bench in there to sit while you take the ride up, very cozy.

 

I still go to the Peppermill Fireside Lounge for the old Vegas vibe

 

Another couple votes for Mandarin Bar and Fireside Lounge at the Peppermill