The journey from Punta Arenas through to Ushuaia was stunning, stay up late in all night light and see the fjords and then get up 3 to 4 am and just enjoy the fjords, glaciers, whales and scenery. Stunning.
Fabulous place. Go on the 4WD excursion, don't even think of doing the train. Expensive, you see absolutely nothing. It should not even be on the option list. Make sure you walk around the town it is delightful.
Cape Horn, well you just have to. It's a big rock at the end of the world but you have got to see it. Puerto Montt, strange place, penguins is fun, cold and windy but really interesting. We encountered a huge iceberg between cape horn and Puerto Montt so keep your eyes open.