What: The largest man-made offshore islands

Where: Dubai, United Arab Emirates

Cost: $3.5 billion

Crux: Two islands built in the shape of giant palm trees. The “trunks” are 5 miles long, each topped by 17 “fronds” up to 330 feet long. A third island group is shaped like a flat map of the globe. Materials: 4.2 billion cubic feet of dredged sand and 50 million tons of rock.