The Faena Hotel does a nicely polished tango show—sequins, smoke machine, Japanese tourists. Only in local salons known as milongas, though, can you glimpse the very heart of the dance. These halls are often in unpicturesque barrios, and the action happens late at night. But for utterly authentic tango, they're worth a trip. Thursday at midnight is popular at the Belle Epoque ballroom of Niño Bien Milonga (1462 Humberto I; 54-911/4147-8687). Experienced dancers also head to Club Gricel (1180 La Rioja; 54-11/4957-7157) Friday through Monday in the neighborhood of San Cristobal. And every day but Tuesday, Confitería Ideal (380 Suipacha; 54-11/5265-8069; confiteriaideal.com) holds matinee performances amid the decaying grandeur of scuffed marble staircases and peeling plaster.