Ushuaia likes to call itself the Southern most city in the world being only 50 miles or so from Cape Horn in the north of the Beagle Channel in Argentina.
Across the water in Chile & 25 miles further south is Puerto Willima which is pretty small with just a few thousand people mostly military, but it is further south!
Ushuaia is a bustling place due tot he ease of which you can fly in from from Buenos Aires & anywhere in the world, and join a yacht or ship for an expedition to Antarctica.
Puerto Williams is much more fun, with only visiting yachts & the best bar in the world. The Micalvi is an old Chilean ship, that was towed in to the creek sinking. which then became its final resting place. It is not the yacht club, which really means it has a great bar, full if yachting history & memorabilia & serves the best Pisco sours for thousands of miles.
Its got a list of about 10 degrees, so your never quite sure if its you, the pisco sours o r the boat thats not right ......