Bob Cassilly built St. Louis’s City Museum from the very stuff of the city. Named for maximum generic effect, the museum is privately owned (half by Cassilly, who serves as creative director) and has no legal connection to local governance. But this mixture of children’s playground, funhouse, surrealist pavilion, and architectural marvel made of found objects has roots in the city deeper than any other institution’s.

“I leaped up and grabbed the guy by the beard,” recalls Bob Cassilly, now 48, who scrambled onto the Madonna‘s marble head to reach the disturbed Hungarian-born geologist, who was perched on a ledge. “We both fell into the crowd of screaming Italians. It was somewhat of a scene.”

Twenty-five years later, Cassilly is creating another ruckus—and scaling new heights—with the nonprofit City Museum he and his wife, Gail, have opened in downtown St. Louis: a fantasia of Cassilly’s own giant animal sculptures, stone trees and caves. Climbing is not only welcome, it’s encouraged (but leave the hammers at home). Since he sold his first public sculpture in 1989, Cassilly’s reputation has grown as rapidly as his work, which ranges from life-size (the hippo fountain in New York City’s Central Park) to fright-size (a 67-foot bronze giraffe at the Dallas Zoo).