The most touristy and, beyond jogging, the slowest way to the park, El Tren del Fin de Mundo originally carted prisoners to work camps. It departs (without the convicts) from the Estación del Fin de Mundo, 8km west of Ushuaia (taxis one way AR$120), three or four times daily in summer and once or twice daily in winter.
The one-hour, scenic narrow-gauge train ride comes with historical explanations in English and Spanish. Reserve in January and February, when cruise-ship tours take over. You can take it one way and return via minibus, though the train fee is the same one way or round-trip.