GPs are prescribing woodland walks to combat depression and treat heart problems under a new scheme by the Forestry Commission.
The Aber Actif Woods project involves woods in Aberystwyth, Ceredigion, and Treherbert in Rhondda Cynon Taf.
The commission urged doctors to use its "natural health service" when it highlighted its plans last December.
Its officials claimed a woodland walk was a better form of exercise than sending people to the gym.
A five-week pilot project was held earlier this year in both areas.
The commission, which funds the scheme, said 80 people took part in sessions during the spring and summer.
Activity leaders are now preparing for a 16-week winter programme later this month.
The free sessions are specially tailored for people with a variety of chronic health conditions such as depression, osteoarthritis, diabetes and heart problems.
They include activities such as Nordic walking, green woodworking skills, bushcraft skills, plant and animal identification, fire-lighting or simply walking in and enjoying the woodlands.
Mair Jones, from Aberystwyth, who has ME, which is also known as chronic fatigue syndrome, said woodland walking had become part of her weekly routine since being referred to the scheme.
"I have gained much benefit in having a regular outdoor activity arranged on a weekly basis," she said.
"It has now become part of my weekly routine and doesn't depend on the weather, as sheltering in the woods on a rainy day with company is all part of the fun."
Zena Wilmot of Coed Lleol Partnership, which is running the sessions, said: "We all know that exercise is good for us, but going to the gym to get fit isn't for everyone.
"This project has shown that walking or being active in woodlands really can improve health and reduce stress at the same time as building interests, developing skills and having lots of fun."