Wiki - Door to Hell (aka, Darvaza gas crater)

The Door to Hell has become a tourist attraction despite the difficulties in travelling there and the dangers involved.

Wiki - Liquid Rainbow

A stream in Colombia is so colorful that it is known as the Liquid Rainbow or the River of Five Colors. Plus, it runs very clear despite the colors.  The Caño Cristales runs through the Serranía de la Macarena in Meta.

Wiki - Manchineel

The world's most dangerous tree is the Manchineel. That gives it quite a reputation. The Wikipedia entry has an Historical Accounts and In Popular Culture section.

Wiki - Oology

The study of bird's eggs is called Oology. The article describes the underground activities of egging, and mentions Colin Watson who was arrested and convicted repeatedly until he died falling from a tree while egging. It also mentions the secret society of eggers, the Jourdain Society, which was raided by the police. 

 

Wiki - Khone Phapheng Falls

The widest waterfall in the world (nearly 7 miles wide). Also, home to the largest freshwater fish in the world. 

 

Wiki - Taï National Park

 

Taï National Park in the Ivory Coast. The fauna list is extensive, with three different types of pangolin. Still, the threatened species are amazing: "Five mammal species of the Taï National Park are on the Red List of Threatened Species: pygmy hippopotamus, olive colobus monkeys, leopards, chimpanzees, and Jentink's duiker."

Wiki - Living root bridge

Trees are amazing. Making a bridge out tree parts doesn't sound exceptional until you see this version where the tree parts are still alive: Living Root Bridge. One of the examples is the Rangthylliang 1 root bridge which is over 50 meters long. The See Also list includes the equally interesting Baubotanik and Fab Tree Hab.