One of this summer's blockbusters will no doubt be Argentine artist Tomás Saraceno's installation on the rooftop of the Metropolitan Museum of Art. The huge, spaceship-like structure is composed of many interlinked, modular spaces through which visitors are invited to climb during 20-minute timed sessions. Each surface is made of transparent and reflective materials, creating a new perception of the environment with each perspective. Note that children must be ten years old and at least 48 inches tall; visit the museum's website for the complete set of entry rules. Ages 10 and up.