Ludwig Mies van der Rohe’s children would surely have happily romped in this less-is-much-more version of the backyard princess castle. Spain-based SmartPlayhouse (smartplayhouse.com/en) is especially proud of its latest design, the Illinois, a nod to the clear influence of the modernist master. The house is lifted off the ground on Farnsworthy exterior columns; marine-grade laminated birch plywood, a thermally insulated roof, unbreakable acrylic windows, and nonslip floors for safe play complete the building. The six-by-ten-foot structure has five-foot ceilings and a 40-square-foot front patio—perfect for a posh play date. The house costs €8,500 (about $11,860), lighting and other à la carte amenities not included. It arrives partially constructed, and then it’s up to you and Junior to raise its walls (or shell out for professional assembly). Your reward? The envy of neighbors for blocks around and a safe bet that your kids will grow up to love elegant, clean design as much as you do. SmartPlayhouse hopes to begin delivering to the United States in 2012.