Buenos Aires is in the midst of a boom of speakeasy—like puerta cerrada (“closed door”) bars and restaurants. Ocho7Ocho, a converted mercado de pulgas, or junk shop, in a residential neighborhood, is one of the coolest. Behind a discreetly marked door in a large, eclectic space—a mix of exposed brick, high stools, and black leather couches—an offhandedly hip clientele sips mojitos and caipirinhas, often until the wee hours (the bar doesn’t open until 8 p.m., but it doesn’t close until 3 a.m. Sunday–Wednesday, and 6 a.m. Thursday–Sunday).