A large glass cube has appeared in Grand Central Terminal, and it isn’t part of the station’s Apple Store. The 10-ton structure is a 21-by-32-foot arena for the world’s biggest squash spectator event. Known as the sport’s Wimbledon, the tournament is the only annual athletic event that takes place in the venerated NYC landmark. Even better, watching the world-class action is free for commuters and passersby walking through Vanderbilt Hall. Enthusiasts, meanwhile, can settle in to catch the action with tickets to the 460-seat temporary stadium. Top international pros face off in the men’s 32-person bracket and 16-seed women’s tourney. Clinics for junior players and an amateur Ping-Pong competition benefiting Big Brothers Big Sisters of New York City round out the weeklong event. For more details, visit tocsquash.com.