I went to Punta Arenas on my ship. It is a nice little town, but not so much there. It is a gateway for cruises down the Chilean Fjords and I know people who have got on 4 day cruises at the last minute for a good price. There was a huge Croatian population here. Some nice homey restaurants (run by locals) with home cooked food. Check them out, they are cheap and fill you up. There is a decent supermarket in the town. It is small but sells essentials.

On my visits to Punta Arenas, I went to both the Penguin Caves and Magdalena Island.
Penguin Caves was a better excursion for me. I did the excursion thru the ship (free). However, from the port you can get a cab to the caves for around $100 US. If you go into the town, you can get one for around $60. There, back and waiting for you at the caves. The admission is nominal to the caves, but the walk from the entrance to the caves is around 1 mile. Please when you get to the caves RESPECT THE PENGUINS. Do not get really close to them, do not go sticking your nose in burrows and talk softly.And if they are trying to get across the path give them lots of space! They will not cross if they think the path is blocked in ANY WAY. These birds are sort of used to people but they are still terrified.

Magdalena Island was an experience. 2 1/4 hour ferry ride out and back. It was so damn rough the day I went. You really need to pick your moment. It was kicking up a gale the day I went so when I got to the island (where there is a colony of 60 000 Magellanic Penguins), I had to keep my eyes closed because of the dust! The rules for these penguins are the same. Please keep your distance.