South of Santiago three hours on Ruta 5 highway is Talca, a medium-sized city of about 250,000 people. From there it's an hour and a half bus ride east (towards the mountains) to get to Armerillo, small town and home of Parque Tricahue, where two friends and I spent a long weekend hiking, eating peanut butter, and somewhat-successfully building fires in our cabin's stove.
We took the train back to Santiago. It was a decent ride, cheaper than the bus, and was reasonably comfortable. Eating Frac (cookies) and peanut butter added to the ambiance.