Nan Madol is an ancient stone city that's located at the eastern coast of Pohnpei, Micronesia. It spans 80 acres, and comprises about 90 man-made islands. Nan Madol
has earned the awe of many archaeologists because the islands are made almost entirely of basalt walls that are 18 to 25 feet high and about 17 feet thick.
Archaeologists estimate that a whopping 250 million tons of these basalt logs were needed to construct the whole city. But the question archaeologists have yet to answer is how these walls were constructed so high, given that each basalt log were can weigh as much as 50 tons.