Olbrich Botanical Gardens. And one of the nicest things about the Garden is that, in addition to having many ferns on the grounds, they have this beautiful cement statue of fiddleheads prominently displayed! I was stunned the first time I saw it, and now it's one of my favorite things to visit in town. I don't know anything about who designed or made it, because I haven't been able to locate a plaque or sign. It's now become a mission to find out the name of the artist who appreciates ferns this much.
Update, March 2010: A former student of mine discovered the identity of the sculptor: her name is Sylvia U. Beckman. Thanks Lois!