First thing, you’ll need a map. You can find one online at the official Subte website.
Different Subte lines are identified with different letters. Line “D” is the line most often used by tourists since it runs through Palermo and Barrio Norte where many tourists stay, along Sante Fe, and into Microcentro.
Cost to use the Subte is 90 centavos per trip. That’s only about 25 cents (USD). You need to purchase a ticket at the ticket booth before going through the turnstiles to the platform. You can purchase a single trip (un viaje) card or a reusable multiple-trip card.
Place the Subtepass into the slot at the turnstile. The machine will read the magnetic stripe and pop the card out the slot at the top. Take the card, then go through the turnstile to the platform.
The machine stamps the date and time on the back of the pass. That way you will know how many trips remain on a multiple-trip card.
The Subte can be incredibly packed at rush hour. In summer it can be unbearably hot.
Trains run from about 5am until about 10:30 at night, depending on the line and whether it is a weekday or a weekend. A complete schedule is available at the Subte website.
Sometimes you might see a person walk through the train and hand everyone a little product like a book or pen, or place it on their lap. This is not a gift. He will come back in a minute to reclaim the product, or you can buy it from him.
Overall, the Subte is a safe and convenient way to move around the city. However robberies and pickpocketing do sometimes happen. But there’s no need to be paranoid. Use your common sense and you’ll be fine.