Often derided as disease-ridden “rats with wings,” pigeons are little loved by many urban dwellers. Sakura Adachi, a furniture designer in Milan, is not among the haters; she admires pigeons for their ability to create private nooks in public spaces. That avian talent inspired her to create a bookshelf called the Cave, which allows readers to curl up in a form-fitting seat, surrounded by their beloved books. The Cave features a blob-shaped, human-size recess at its base. Sitting in this upholstered niche is supposed to make a reader feel secluded — akin to being lost among a college library’s dusty...