to get to Ushuaia from Puerto NAtales in Chile, you have to take a 4 hour bus ride to Punta Arenas. From there on you will probably have to stay the night over in Punto Arenas as busses from Ushuaia leave only a few days a week, more or less three times a week. From Punto Arenas you will then leave with the bus in the morning and spend the whole day driving and waiting to cross with the boat, then cross borders and arrive in Ushuaia in the evening. It is about a 12hours bus ride from Punta Arenas... a real hassle!