Ushuaia is the southernmost city in the world. If a city needs at least 50,000 people.
If the minimum is 100,000 people, it’s Punta Arenas:
Reduce it to 1,000, and Puerto Williams wins.
It might depend on your nationality.
Punta Arenas and Puerto Williams are in Chile. 
Ushuaia is in Argentina. 
I went overland from El Calafate to Ushuaia in the spring of 2005.
There was a ship in the harbour, about to leave for Antarctica. They were offering discounted passages but I couldn’t go because it was towards the end of my trip and I had to get back to Perth.
I kind of regretted that, but just over two years later, I was back in Ushuaia.
This microbrewery was on the outskirts of the city. The cushions lay over thermally heated benches.
It looked out onto the Beagle Channel:
This was the channel at dawn:
