Nanji was an island, where the daily trash from Seoul used to be dumped for 15 years. 92 million tons of garbage resulted in two massive mountains of garbage measuring over 90 meters in height. In 1993, the city government decided to close the site, and mainly due to the smell, they covered the huge mountain with 1 meter of soil.
After years passed, plants started growing, flowers were blooming, and the mountain became the house of many animals.
It re-opened as a eco-friendly park in 2001.