Sangumburi (산굼부리) is a crater with a circumference of over 2 km, and has been designated as a Natural Monument. It is located on the southeast side of Jeju-si, and is a flat crater, about 650 meters wide, 100 meters deep, and 2,070 meters in circumference. If you look at the crater from above up, it looks like a man-made circular stadium. 
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