As collector Jochen Raiß hunted flea markets and antique stalls for three decades, he noticed an odd trend: anonymous photographers captured women posing in trees. A hardcover edition from Hatje Cantz explores this curious phenomenon, published both in German and English.

The mystery of why these women are up there—could it be a forgotten sport or just a quirky pastime? The collection is as much fun to speculate about as the images themselves.

Swiss newspaper Züricher Tagesanzeiger asked, "What are they all doing up there?" And German paper Der Spiegel suggested the climbing might be a “forgotten popular sport.”

Fans can purchase the book on the publisher’s website to find out more about this arbor-climbing craze. Perhaps it is time for an urban exploration in the trees?