Ever attuned to people’s needs, Frederick Law Olmstead, the 19th-century visionary architect behind Boston’s 1,100-acre “Emerald Necklace” park system, would have appreciated some of its 21st-century priorities.

“Its year-round restrooms,” laughs Mergel, the James & Audrey Foster Executive Director of the Esplanade Association. “Restrooms are key.”

This fall, after two decades of planning and slightly more than a year after breaking ground, the Charlesbank campus and Smith Family Pavilion will be finished. At $24 million, the project is the biggest privately funded state park initiative in Massachusetts, and a long-anticipated new facility for residents and visitors. It’s also a crowning achievement for the Esplanade Association, which celebrates its 25th anniversary this year.