Really sweet imbibing stop that is an absolute must if you are staying downtown, and a place you should strongly consider visiting even if you're staying on the Strip. It's just a short walk down from the Fremont Street Experience on a delightfully sketchy block. (I was there late afternoon on a summer's day so it was still full light outside; I suspect the area would seem slightly murder-y after dark.) It has the iconic neon sign outside and inside still maintains that mid-century vibe, even though the floors have been redone with an engineered hardwood. There's a nice curved cutout in the ceiling which defines the bar space from the table seating space. The bar itself is a long L-shape and would seat at least a couple of dozen people. They have good beer and some neat cocktails and it's served up by cool bartenders who know what they're doing. It's an excellent atmosphere and soaked in history. If the Fireside Lounge at the Peppermill were hipper and had better drinks, it would be Atomic Liquors.
Side note, they don't actually sell package liquors; this is a cocktail lounge only.