A seven-hour, $70 architectural tour may seem like a bit much. But when the Chicago Architecture Foundation hosts an authoritative, metro-area-spanning tour of local treasures designed by Ludwig Mies van der Rohe, no expense, nor square inch, is spared. The motorcoach expedition begins at the twin residential skyscrapers of 860-880 North Lake Shore Drive, heads to the Loop for the Federal Center and the IBM Building, and then turns south to the Illinois Institute of Technology for a look at the newly restored Crown Hall. The tour's apex is on the Fox River at the Farnsworth House: a minimal, one-story steel-and-glass cube that appears to float on its idyllic site, embodying van der Rohe's famous aphorism, "Less is more."