here are a handful of pics from the holden arboretum, outside of cleveland. just doing a quick search before i uploaded it, this arboretum was a creation of a philanthropist who almost left his trust to the harvard arboretum, but was convinced cleveland could use one. it almost never came to be!
there is 3600 acres i guess. there are a couple pics from atop this rather large wooden tower structure-gives a great view! and also from this kinda tree canopy caged bridge thing(sorry i didnt get photos of the structures)