1 1. Kansai International Airport

Osaka, Japan

Background:

Land is a scarce resource in Japan, so engineers headed roughly 3 miles offshore into Osaka Bay to build this colossal structure. Work on the manmade island started in 1987, and by 1994 jumbo jets were touching down. Travelers can get from the airport to the main island of Honshu via car, railroad or even a high-speed ferry.

Why It's Unique:

Kansai's artificial island is 2.5 miles long and 1.6 miles wide—so large that it's visible from space. Earthquakes, dangerous cyclones, an unstable seabed, and sabotage attempts from protestors are just some of the variables engineers were forced to account for. As impressive as the airport is, Stewart Schreckengast, a professor of aviation technology at Purdue University and a former aviation consultant with MITRE, cautions that climate change and rising sea levels pose a very real threat to the airport's existence. "When this was built, [engineers] probably didn't account for global warming," he says. "In 50 years or so, this might be underwater."