As the empirical evidence mounts, nature-as-medical-treatment is catching on. “Ecotherapy” is a burgeoning field, and some doctors even write prescriptions for time spent in parks, as my colleague James Hamblin wrote in 2015.

In some ways, this is a return to an 18th- and 19th-century understanding of what the body needs. Old-timey therapies that suggested patients go for walks outside or “take in the sea air” were on to something. The pioneering nurse Florence Nightingale advocated strongly that patients be exposed to fresh air and sunlight. As she wrote in her 1859 Notes on Nursing:

It is the unqualified result of all my experience with the sick, that second only to their need of fresh air is their need of light; that, after a close room, what hurts them most is a dark room. And that it is not only light but direct sun-light they want… People think the effect is upon the spirits only. This is by no means the case…Without going into any scientific exposition we must admit that light has quite as real and tangible effects upon the human body.

The light certainly feels tangible here, snuggled in the bosom of the Rockies. There are still stripes of snow on the mountains, which are peppered here and there with fistfuls of pipe-cleaner pine trees. There is a sparkling lake in the valley, and the rushing sound of a hidden waterfall off to our right. The morning mountain air is thin and cold, but fresh, and the smell of pine is so strong that it seems fake. It smells like someone has strapped a got-dang Yankee Candle to my nose. I discreetly sniff the woman next to me to be sure she’s not just wearing a really strong perfume.

All of this is distracting, Williams says, from any ruminative, negative thoughts I might otherwise be having. She references a study that had people take a 90-minute walk either in a natural environment, or in an urban environment, scanning their brains before and after. The people who went on a nature stroll had decreased activity in the subgenual prefrontal cortex, which is associated with rumination—the sort of negative thoughts that you return to over and over, picking at a scab. And the participants reported feeling better, as well.

Williams says she copied Michael Pollan’s “Eat food, not too much, mostly plants” axiom for her own prescription: “Go outside, go often, go with friends, or not.”

But the problem is that this rash of research showing how wonderful nature is for you is coinciding with a decrease in the amount of time people actually spend in nature. “Our culture tells you that watching Netflix or eating ice cream will make you feel great, and those things are great, but many of us in our society are very disconnected from nature,” Williams says.

A 2008 study found that the percent of Americans who participate in outside activities like camping, fishing, or hunting has been decreasing by about 1 percent a year since the late 1980s. A survey done in the U.K. found that 70 percent of adults remembered doing most of their “adventurous play” outside, while only 29 percent of kids said the same. And, at least in 2001, when the Environmental Protection Agency did its National Human Activity Pattern Survey, adults spent 87 percent of their time indoors in buildings, and another 6 percent of their time in vehicles.