No sunlight reaches the bottom of the Mariana Trench, making it pitch-black and frigid. “As you descend, the inside of the sub gets colder and colder, so you have to add on layers of clothing to keep warm,” says Amanda Demopoulos, a scientist at the U.S. Geological Survey. Cameras and tiny portholes allow researchers to gaze into the depths, lit only by the sub’s headlights. The Mariana Trench is home to many unusual species, like anglerfish, amphipods, and ghostfish. “The deep sea continues to be a new frontier for amazing discoveries,” says Demopoulos.