From the air they look like gigantic slices of citrus, waiting to be dropped into a cool glass of sangria. In fact they're a section of the Garden of Sensors, created by French "agriculture artist" Jean Paul Ganem near Montreal's Dorval Airport. Look closely and you'll see how the site got its name: those raised metal objects at the center of each circle are biogas sensors, which capture methane from the 247-acre landfill that is now covered by Ganem's geometric floral plantings. You don't have to fly into Montreal to appreciate the full scope of this monumental work. Just visit Ganem's Web site, jpganem.com, where a video will give you a bird's-eye view and then zoom in for closeups.