Farnsworth House, Illinois

The Farnsworth House in Illinois, designed by Mies van der Rohe in 1951, is a 1,500-square-foot glass box suspended on eight steel columns above the Fox River—a radical departure from #4 Villa Leopolda's sprawling 18 acres. Every interior element is visible from outside, embodying the maxim 'less is more' with a cost of $74,000 in 1951, equivalent to $900,000 today. Its 30% lighter footprint compared to the typical modern mansion makes it a UNESCO candidate site, drawing 20,000 annual visitors.