I would like to make the case for what I think is probably the most impressive and beautiful architectural "wall": Michigan Avenue in Chicago across from Millenium Park down to about Roosevelt Avenue.
there is a relative consistency of scale but an extremely wide variety of architectural styles from a kind of strange neo-Gothic through Sullivan's Gage Building, International style and Beaux Arts. The open space of the park - dedicated as open space and carved out of the old railyards, makes a sharp contrast to the building's vertical edge. All of these buildings then face across the park to the truly vast expanse of Lake Michigan, and by extension, the East. Metaphorically traveling from the established financial and commercial capital cities of the east coast, Michigan Avenue was the face of Chicago, proudly standing in a hard line. It may be the most significant and tallest cliff in the hundreds of miles of flat lake and prairie.