In 2011, archaeologists rediscovered a "gate of hell" at Hierapolis, Turkey. This stone doorway led to a small cave filled with a visible mist. It sits in a geologically active zone, with a deep ...

The complete opposite, if you consider the age of its formation, is the "gate to hell" in Turkey. It is also called the "Pluto's gate." It was discovered in 2013 but dates back to antiquity.