The subte (subway) is one of the quickest ways to get around. Packed trains mean it's not always the most comfortable, though it's generally fairly safe. Most stations are reasonably well patrolled by police, and many are decorated with artworks. You'll likely hear musicians and see actors performing on trains and in the stations.
Monday through Saturday, the subte opens at 5 am and shuts down sometime between 10:30 and 11 pm, depending on the line; on Sunday, trains start at 8 am and stop between 10 and 10:30 pm. Single-ride tickets to anywhere in the city cost 5 pesos; you can buy passes in stations for 1, 2, 5, or 10 trips or use a rechargeable SUBE card.
Línea A travels beneath Avenida Rivadavía from Plaza de Mayo to San Pedrito in Flores.
Línea B begins at Leandro Alem Station, in the financial district, and runs under Avenida Corrientes to Juan Manuel de Rosas Station in Villa Urquiza.
Línea C, under Avenida 9 de Julio, connects the two major train stations, Retiro and Constitución, making stops along the way in Centro and San Telmo.
Línea D runs from Catedral Station on Plaza de Mayo to Congreso de Tucumán in Belgrano.
Línea E takes you from Bolívar Station on Plaza de Mayo to Plaza de los Virreyes in Flores.
Linéa H, the subte's newest line, is only partially open. It runs from Corrientes through Plaza Miserere in Once to Hospitales Station in Parque Patricios, crossing lines A and E; eventually it will extend north to Retiro, crossing lines B and D.