South America's marble cathedral carved by nature
bbc.com
bbc.com
Was it worth it? Yes, absolutely beautiful, not touristy at all, met a couple in there 70s who had driven through Africa, which included the DRC. Mount Fitz Roy, Chaletan, although beautiful are too touristy. Everyone speaks english, they accept euro/usd, doesn't feel like you're actually in Argentina.
I guess the easy version might be Carrara, Tuscany where marble has been mined for millenia. You can drive around the hills above the city on roads carved into and through the marble accompanied by dusty trucks laden with giant blocks.
However, it is true that in general it is not an easy area to travel through (and that's part of what makes it raw and unique). If you don't have a car, hitchhiking can be a lot more reliable and faster and the local buses between small towns.
As for mountains they are literally in every region. Before you hit Patagonia there is lots to see in the Los Lagos region, be sure check out the Valdivian rainforest, it's amazing! https://en.wikipedia.org/wiki/Valdivian_temperate_rain_fores...
Not to mention that just west of Santiago you find Valparaiso which is definitely worth another day or two of your time if you like urban environments.
If you do spend a day or two in Santiago, it's fun to go to the Bio Bio market or la Vega indoor food market. (watch your bag and your pockets)