Located in the Jaua-Sarisariñama National Park in Venezuela are some of the biggest sinkholes in the world. The sinkholes are 350 meters wide and 350 meters deep and are a geological mystery. The huge vertical walls have created an isolated ecosystem, with completely unique species of both flora and fauna. They’re so isolated in fact, that the sinkholes were only discovered in 1974. The scientific expedition was documented in David Nott’s book “into the lost world.”