Mostly I wanted to cover this because at some point I got some maps for it.
This mall, which I first read about at Labelscar a long time ago has its origins in the 1916 Plankinton Arcade, a two-story (plus basement) structure that added offices on top in the 1920s. Other history is quite spotty though...there was a renovation in 1936 and a downturn in downtown closed most of the businesses there by the early 1960s.
In August 1982, the structure was incorporated into Grand Avenue Mall which combined a number of other businesses into one cohesive structure. To the west was the 1900 Boston Store (owned at the time by the pre-Macy's Federated Department Stores, which owned a lot of the nicer regional department stores at their peak—Burdines, Foley's, Bullock's, Rich's), then the "New Arcade", a three-story structure with the "Speisegarten" level food court on top and incorporating another office building with a Walgreens, and to the east, linking Plankinton Arcade to the original Gimbels.
The maps for these three levels can be found here (from Google News Archive): Street Level, Skywalk Level, Speisegarten Level, and the Store List.
Well, as you can expect, the mall did well initially but started to fall off as downtown Milwaukee deteriorated (it took about ten years). One of the first to go was Gimbels in 1986, a result of parent company BATUS dismantling the chain, with the store reopening as Marshall Field's by the end of the year. Marshall Field's closed in 1997...though that same year the International Clown Hall of Fame moved into the basement.
Around the early 2000s the mall was refurbished with new paint and "a ton of icky graphics along the food court in bright pinks" (see this Labelscar picture). I believe this is when some of the allegations of mismanagement (see Labelscar comments) happened, as the timing lines up for some of the misfires, like installing a Warner Bros. Studio Store (and not renewing local tenant ToonVille's lease) right before the newly created AOL Time Warner decided to pull the plug on the entire chain. The first level of the Plankinton Arcade was turned into Linens N Things and T.J. Maxx, both of which took up all the inline space. The former Marshall Field's was converted into a Borders Books & Music and a Residence Inn.
Sadly, I can't find much more information on what happened to the mall beyond that. Linens N Things closed in bankruptcy in the late 2000s with Borders a few years after that...and after the demise of the The Bon-Ton Stores (which Boston Store had been a part of since 2006, along with sister stores Carson Pirie Scott, Bergner's, Younkers, and Herberger's) the mall was converted into The Avenue, which added a food hall on the first level while turning the old third level food court into office space. Unfortunately, I can't see how this is laid out, though the lease plan shows the "New Arcade" to be largely gutted.
