1) During Prohibition, an illicit liquor store or nightclub.
2) Not-during Prohibition, a sexy place to grab drinks behind a storefront that gives the impression that it is not, in fact, a sexy place to grab drinks.
For example, The 18th Room—an elegant place for imbibing from Dave Oz of Bathtub Gin, open now, right next door to Bathtub Gin.
You'll find it behind a faux coffee supply store (note: not the actual coffee shop that hides Bathtub Gin). It's not a coffee supply store at all, you see. It's an intimate '20s-inspired space flush with velvet booths, tropical walls, and brass details, playing either jazz or swing or something in that vein, ready to ply you with expertly crafted cocktails—which is just about 98% more useful and exciting.
Now, come with a date. Say good evening to the host, who will quickly build you a guest profile with your flavor and spirit preferences—soon to be sent to the bar team, who will, in turn, make you a bespoke cocktail on the spot.
Should you go the more traditional route of choosing a drink that already exists, know that the cocktails here were crafted by a cocktail guru known as Joseph Boroski, and he's created things like the Nailed It! (whisky, carrot whisky liqueur, house-crafted chocolate fudge, smoked salt) and the Un-Pulped Fiction (coconut oil-washed rum, caramelized pineapple shrub, fresh lime, macadamia nut).
There's no site or social at the moment, so this slideshow is essentially all you've got. Get in there.
The 18th Room, now open, 134 9th Ave (at 19th St)