This looks like a normal area of the loop but behind the black doors there is a piece of little known Chicago history. Looking thru the cracks above the doors you can see part of this 10' wide, 18' high and 177' long path that is forever deeded to be a cow path. Thats right a cow path in the Loop. This all started back in 1844 when the landowner Willard or William Jones (depending on the source) started selling off his land but wanted to be sure that his cows always had access to pasture so he deeded the land that way. Safe to say the pastures are gone and buildings slowly built up and around the path but the deed restriction preserved this little oddity from construction.
The only difficult part of this will be grabbing and replacing the cache, there may be muggles in cars parked at GZ or at a stop light, muggles on foot and even muggles in restaurant windows which look directly out at the cache.
Next time you see a cow wandering in the loop it might just be heading here.
Thanks to tzinny for posting the note on how to see more of the path. While on LaSalle you should see an alley that is between Madison and Monroe, head east and look for a Burrito Beach restaurant and from there you can get another look at the path.
Congrats to contact dermatitis on the FTF!