If you're thinking about a cruise to Antarctica, there's a good chance that your boat will leave from the southern tip of Argentina, from a small port city of Ushuaia. It's worth getting there a few days before your boat departs. For one thing, flights to Ushuaia don't exactly arrive and depart several times a day. If your flight is canceled or your checked baggage disappears, you're not going to be able to go from the plane directly to the boat--or worse yet, you might miss the departure entirely.
The town of Ushuaia, itself, is not a big deal, but the surrounding area of the Tierra del Fuego is gorgeous and has some amazing opportunities for easy to moderate hiking The Tierra del Fuego National Park has many well-marked trails, though having a guide with along wouldn't be a bad idea. You could also do a relatively easy day hike to the Martial Glacier. There's a chair lift up the side of the mountain (in the cold months, the area becomes a ski resort), and from there, you can hike further up for some amazing views.
There are also day hike trails around Lagos Escondido and Fagnano and we did one short hike with a guide to see a big beaver dam. Beavers aren't native to South America, but in the 1940's someone brought a few to Argentina from Canada, thinking they'd establish a fur trade, and the little critters started taking over. Over the past several decades, they've become an invasive problem--they fell trees, build dams and lodges and wind up flooding the pristine forests of the area. Conservationists are trying to trap and remove the beavers, but until they're under control, you could take an easy hike to see them, and to understand how damaging their introduction to the area has been.
There are some other fun experiences in Ushuaia, aside from hiking. You could visit the southernmost post office in the world, and send a postcard (remember those) to your friends and family. You could also stand at the southern end of the Pan American highway, and contemplate what would be involved if you drove all the way to Alaska.
Or, if you're there at the right time of year, you could park yourself at a bar overlooking the Beagle Channel to watch the sunset off to your right, and then watch the glow of the sun travel in a backward direction across the horizon until the sun rises, just an hour or so later off to your left.
Whether you're continuing onto an Antarctic Cruise, or just enjoying the beautiful scenery of the Tierra del Fuego, you'll have lots of great hiking options using Ushuaia as your base of operations.