Vallecitos is a popular valley for Aconcagua altitude preparation. It’s close to Mendoza (Argentina), the refuge is reachable by car and it has peaks almost up to 6000 meters.
I can’t say much about the peaks (as I climbed only two of them), because I got caught by pretty bad weather. There was even snow fall on the first day of summer. But I can attest it’s really beautiful and I hope to go back there one day.