These high altitude hostels are all definitely worth the walk:
Refugio Frey: Frey is probably the biggest and most well-known refugio. It's located in the ski center Catedral and is the only refugio in the area open year round, with great skiing in the winter and great biking in the summer. High granite "fingers" create a climber's paradise and travelers flock from around the globe for some of the best climbing in South America. Frey, perhaps more than the other refugios, seems to host a kind of community. People come and stay for stretches of days or weeks versus simply passing through.
View from Frey
Dusk walking around FreyRefugio Lopez: Lopez is a great refugio to visit if you're short on time. The entrance to the trail is located close to the picturesque Colonia Suiza, a quaint little village with a market that has an array of local handiwork and food. The market is open on Wednesdays and Sundays and I HIGHLY recommend the waffles with raspberries and cream or dulce de leche and cream. Lopez is a relatively short climb that takes you up to amazing views overlooking the Lake Nahuel Huapi. You don't really need to do an overnight stay at Lopez because it makes such an easy day trip.
View from LopezRefugio Italia: This refugio is located at Laguna Negra. The entrance for the trail up to Laguna Negra is also close to Colonia Suiza, but the trek is longer than that to Lopez. However, the majority of the trip is through the forest along a relatively flat plane. Only the very end gets steep and rocky. Refugio Italia is hidden away next to an impressive--you guessed it--black lagoon. Reward yourself with an artisanal beer after your hike brewed in the refugio.
Refugio Italia at Laguna Negra