It’s only a short walk from the Longwood Medical Area, but for anyone spending long hours roaming sterile hallways breathing through surgical masks, Riverway Park can feel like another world — especially during its yearly transformation by Studios Without Walls. More than 20 members of the Brookline-based professional artist collective have turned pathways along the Muddy River just north of the Longwood T stop into a vibrant outdoor sculpture garden of multimedia site-specific works. Through Sept. 4, those who wander the park can see Rebecca McGee Tuck’s giant mushroom, with its multicolored cap of discarded single-use plastic strips, Gail Jerauld Bos’s and Ruth Rosner’s fanciful figures suggesting humankind’s whimsical accumulations on our journey from cradle to grave, and other works.

This year’s theme is “The Ground We Walk,’’ reflecting the history of the land’s inhabitants. It also honors the 200th birthday of Emerald Necklace visionary Frederick Law Olmsted. “The ground we walk is the ground he walked,’’ says SWW founder Bette Ann Libby, adding that the exhibition is designed not only for contemplation, but also to promote conversation and engage. Many of the works are interactive through light, sound, or movement, and on-site maps contain clues to an art treasure hunt — see if you can identify pieces based on clues the artists provided.

Studios Without Walls members are professional artists, some of whom have exhibited internationally. As a collective, they’ve been curating these free outdoor exhibits since 1999. “It’s a privilege to be part of this group — I love it,’’ says longtime contributor Janet Kawada. “It’s a nice camaraderie, and every year it gets more exciting.’’

Each year’s exhibit is planned by Libby and a small core group (Kawada, Jamaal Eversley, Gail Bos, and Maria Ritz this season) and encompasses a different group of participants. “There is more diversity each year,’’ Libby says, “young artists and new energy, immigrants from Argentina, Japan, Israel, and France.’’

With support from a number of organizations, including Brookline Parks & Open Space, Brookline Community Foundation, Brookline Commission for the Arts, and Mass Cultural Council, SWW offers participants a modest stipend toward costs of material, fabrication, and installation. However, the creative labor is an act of love, not to mention imagination and ingenuity — each work has to be made to withstand the vagaries of weather and mischief.

Conservation is a major thread in “The Ground We Walk,’’ and this year’s artists are masters of recycling and clever repurposing, like Max Bard’s high-hanging “Red Flag,’’ a pictorial representation of contemporary Massachusetts made from wood and litter he collected from wild spaces around the commonwealth.

History is reflected in Liz Helfer’s “Standing Still,’’ a woven QR code that you can scan to see archival images of the park, and in “Message in a Bottle,’’ by Libby and Janet Kawada, a delicate vessel filled with old bottles. It urges viewers to wonder how the relics were once used and who used them — and perhaps slip a message of our own into one of the bottles. Allen M. Spivack reflects the ground we walk by recalling those buried beneath it, especially victims of genocide. Amidst a garden of brilliantly hued flowers rise disembodied hands reaching for the sky.

Many works reflect not just loss but also resilience. “Ties That Bind’’ is a gorgeous hanging textile woven from hundreds of shoelaces by collaborators Stacey Piwinski and Mihoko Wakabayashi — with the help of area schoolchildren. “Collecting laces from the community, we worked together to weave them into this safety net of support for one another,’’ the signage reads. Richard Dorff and Rachel Shatil’s “Lost and Found’’ is a red-hued river of donated shoes leading from the path up into white cloud-like mesh in the boughs of a great oak, leading the eye from the shaky ground we walk, as Shatil writes, toward “a softer place, where we can rest, connect with our losses, and connect with ourselves, while [lying] peacefully in the cradle of our imagination.’’

Through the exhibition, artists can reach a wider range of viewers than might come to a formal gallery, and many visitors return year after year.

Libby says, “I want them to stop, breathe, get out of their normal space of stress and anxiety, and look at the world in a different way. There are a lot of very powerful statements here, but it’s unintimidating in this special natural environment. It makes you feel good.’’

Karen Campbell can be reached at karencampbell4@rcn.com.