Sacred Retreats of California (2013)
nytimes.com
nytimes.com
I was entertained that the author could not imagine anything more austere than heat, running water, and a shared telephone.
Here's a cheap tip for a stunning California retreat. Go to Yosemite, skip the valley, and spend a few days backpacking in the less-trafficked parts like Hetch Hetchy or Wawona. You won't have heat or the public telephone, though ;-)
Applying some common sense, they probably mean 'for off-the-grid austerity [in commercial retreat accommodation available in the US]'.
For a less financially-focused treatment of this very real topic, please see "Visionary State" by Erik Davis
The Visionary State: A Journey Through California's Spiritual Landscape
https://techgnosis.com/category/podcasts/
Highly recommended for anyone interested in religion, spirituality, mysticism, gnosticism, counterculture, high weirdness, psychedelics, or the occult.
Tassajara is a place I plan on returning too. My first trip, I was doing a retreat and engaged in some of the chanting and meditation -- it took awhile to get used to it. I also explored the tubs, the grounds, and used the complete disconnect from communication to let myself just relax, calm down, and renew a bit. The food was very good. Being based in a valley between a set of hills, the heat can be quite intense during the day.
Getting away to day, for me, are the mountains and deserts and more remote areas of California. I have lakes I can be on in 20-30 minutes, lose myself at a mining claim exploring for hours and days, or hot springs in the eastern sierras mere hours away.
Most of the grounds mentioned, I've been to a number of them. They are quite amazing. There are places you can go on your own and find unique experiences and relaxation.
https://en.wikipedia.org/wiki/Eknath_Easwaran
https://www.bmcm.org/about/about-eknath-easwaran/