What is three-dimensional and has six equal, square faces that all meet at right angles? Yes, a cube. It’s been the subject of many mathematical challenges, and puzzles such as the Rubik’s cube. In the Star Trek series, the Borg cube is the frightening hive starship of the Borg Collective. It’s a prison-black no-exit endgame. And then there are Larry Bell’s glass cubes (and rectangles)—transparent, translucent, reflective, frosted, sometimes colored, sometimes stacked or in nesting multiples. Bell, a master of Conceptual art who is now in his mid 80s, believes that “all artwork is stored energy,” and describes his own art as “the interface of light and surface.” This fall and winter, until March 15, six large sculptures by Bell will “activate” the lawns in Manhattan’s Madison Square Park. The works have a collaborator in the weather, which likes to press its nose against glass. —Laura Jacobs