So here we go. Something about buying a dual-sport has made me want to seek out urban refuges, and this one captivated me. Clues:
--It's inside the perimeter
--It was built in 1906
--At one time was an indoor pistol range
--It was dynamited in the 60s
Though there are trails & I rode em I'm not clear if it's cool to ride in there. There's an approach from a different direction that I think is used by people on foot or bike, so I'll allow any latitude you want in getting this one (pics from the entrance, say.) Anyway this should be a fun escape to a part of Atlanta you haven't seen.
From David Kaufman's book Peachtree Creek here's a photo that shows (at the right edge) the tower that's visible behind my bike in the 1st pic.
That's enough clues for now, methinks.