The quietest place on Earth is a room in Minneapolis, Minnesota, and the longest anyone has stayed in the dark there is 45 minutes. The 'anechoic chamber' at Orfield Laboratories absorbs over 99 percent of sound with 3-foot-thick fiberglass wedges and insulated walls, removing virtually every sound except that of people and objects brought into the chamber. In some cases, that's used for simple industrial purposes: it's a way to hear the sounds of switches, motors, or washing machines without outside interference.
Put a human being in there, however, and they become disoriented or even experience hallucinations. After a few minutes, founder Steven Orfield told the Daily Mail, your body begins to adapt to the soundlessness, picking up smaller and smaller sounds. "You'll hear your heart beating, sometimes you can hear your lungs, hear your stomach gurgling loudly. In the anechoic chamber, you become the sound." Because there are no external sounds, it's difficult to move around: "If you're in there for half an hour, you have to be in a chair."
In extreme cases, the sensory deprivation is debilitating. NASA astronauts train by being placed in a water tank in the room, an experience that apparently causes hallucinations as the body tries to create sensations out of thin air. When the lights are turned out, the Mail says that the longest time anyone has been able to stay inside is 45 minutes. At Orfield, it seems, the greatest distraction of all is not noise but silence.