Some mystery before the martini: To access Washington's most exclusive watering hole, patrons who have reserved in advance navigate a dark bar called the Passenger and two more doors after that. The last one slides open to reveal just 18 seats in a candlelit cocoon of civility, where shelves of herbs and spices suggest an apothecary and the loudest sound you're likely to hear is that of a handsaw against a block of crystal-clear ice. Derek Brown, the bar-within-a-bar's dapper and scholarly master of ceremonies, takes details such as ice seriously; to watch him shake a drink is to discover, if you don't already know, that the shift from arm to arm, the push and the pull, isn't just good theater but the proper way to introduce spirits to chill in a container. Great ingredients, superb craftsmanship, a bit of lore with the liquids: It all adds up to some sublime sipping. (Pleasing snacks are whipped up by Javier Duran, the former sous-chef at Cork Wine Bar.) There's no menu, by the way. The price of admission involves three cocktails, starting with a light welcome, perhaps champagne or a vintage punch; continuing with something seasonal or of interest to Brown; and concluding with a libation based on your conversation with him. Brown's current favorite? A twist on a Manhattan, kicked up with celery bitters. The drink he most loves to make, and continues to refine? A dry martini. Here's to tasting him practice.