If you’re planning a trip to Torres del Paine, you will probably want to spend a night before and/or after your trek in Puerto Natales. There are several plusses to doing this, including the fact that you can usually leave excess gear in your hostel for the duration of your trek, taking a good amount of weight off your back.
Though there’s not a ton to do in the city, you can easily fill a day with wandering around, stopping by the grocery store, and enjoying a nice meal.The Unimarc grocery store on Manuel Bulnes and Baquedano is a good place to stock up on food for your trek. There’s also a dried fruits store called 40 y 20 Frutas.
If you want a hearty meal before taking off on your Torres del Paine adventure, I recommend checking out La Mesita Grande (Arturo Pratt & Eberhard), a yummy pizza place with a long menu. If you're stopping by after your trek, you should definitely reward yourself with one of their delicious dessert pizzas!
There are several hostels in Puerto Natales, but we highly recommend Kaweskar Backpackers’ Hostel. Run by a cool dude named Omar, the place is homey, comfortable and clean. They also rent camping gear for those who need it. Just be forewarned: while you may show up with your Torres del Paine itinerary all planned out, Omar knows best. Let him help you rearrange your trip (if necessary) to get the most out of it. He’s hiked the circuit more than 25 times, so I think we can trust him.
Buses leave for the park only a few times a day, and if your arrival in Puerto Natales doesn't perfectly coincide with a departure to the park, you'll have to stay in the town. So, it's best to plan for that ahead of time and give yourself some leeway. No need to spend more than a night in Puerto Natales on either end of Torres del Paine, but it's worth a stop to avoid rushing.
There is no central bus station in town, so most of the bus companies stop somewhere along Baquedano, one of the main roads, at their individual storefronts. You can also purchase your bus tickets out of town here.