We were passing through Atlanta this day and were in the park the same time you were! I carefully looked through your photos to see if I recognized any familiar scene, but didn't make a connection with any. It was just as beautiful as your pictures portray!
Piedmont Park was redesigned by the Olmsted Brothers in 1903, or something like that. It fell into major disrepair for a few decades, and then the Conservancy was formed and has since injected something like $80-90M into the park in the last 20 years. I live in a highrise (which you can't see) a few blocks away. The park is also ringed by mid-rises of 5-10 floors, which you can't see because of the trees. It's probably the only place in the south that is truly "big city". Atlanta also has several other equally impressive parks - Centennial Olympic, Grant, Chastain, Old Fourth Ward, heck even Stone Mountain out in the burbs. I feel fortunate to live here. Thanks for the photos!