On the east side of Red Square, this famous store is actually a series of long arcades connected by cross passages. It instantly reminded me of Milan's Galleria, but I like GUM far more because of its lightness and access to the stores through its interesting passageways.
This view is along one of the arcades. Each of the arcades is 3 floors high. There must be hundreds of stores here.
This, for example, is the Clinique boutique.