Sierra de la Ventana
Sierra de la Ventana is a town in southern Buenos Aires, Argentina. There's plenty of camping, and porteños tend to come here to get out of the city for a long weekend. The train from Buenos Aires capital to Sierra de la Ventana costs 95 pesos (as of November 2014), goes all night, and is not very comfortable.
South/East toward Bahia Blanca
There's only one road out, and you can easily walk there from the center of town. There's a speed bump (lomada), and locals hitch from there all the time to go to Saldungaray, 9 km away. Saldungaray is tiny and also only has one road leading out, and cars pass slowly and have plenty of room to stop at that spot, so it's worth it to get a ride to Saldungaray.