Madagascar, Tsingy. These knife-like limestone formations stretch over 70 meters into the air. Known as The Forest Of Knives, these razor-sharp limestone points can slice through equipment and flesh easily, which makes traversing them extremely difficult and dangerous, some climbers have been known to get through over 15 pairs of boots! It is estimated that the Tsingy has the largest underground cave system in the world and many animals live among the endless maze of disorienting corridors, humid caves, and unforgiving razors at the ground level.
(Image one credit: Pierre-Yves Babelon)