If you were asked where the most silent place on Earth is, you might respond Antarctica or somewhere in the Sahara Desert, but you’d actually be wrong.

It’s in Minnesota—where among the many buildings of Orfield Laboratory lies the Anechoic Chamber, a place so scientifically configured to absorb sound, that a mere blink becomes deafening.

The ambient noise inside the Anechoic Chamber is at negative decibels—minus-24.9 dBA to be exact—which is a Guinness World Record and so quiet that it’s actually below the threshold of human hearing. With zero sound of any kind, visitors, who sometimes can hardly stand the silence, report hearing their body’s minute functions like blood pumping and eyes blinking.

“When it’s quiet, ears will adapt,” Steven Orfield, the lab’s founder, told the Daily Mail’s Ted Thornhill in 2012. “The quieter the room, the more things you hear. 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.”

Part of what creates ambient sound is the reflection of it on walls and glass—the typical stuff rooms are made out of. If one steps into a foam-lined recording booth, they may notice the audible sound levels drop or seem significantly muffled: that’s because the foam is inhibiting the reflection of soundwaves; but some are still able to bounce off and create sound.

The Anechoic Chamber is a steel box suspended on springs inside a larger steel box. The interior box is lined with brown fiberglass ridges of different sizes that completely neutralize soundwaves of all different frequencies coming from any direction. These ridges even cover the floor, and so visitors stand on a suspended mesh.

Orfield says that some people, probably city dwellers, can’t take it for long. The typical tour is 90 minutes, 20 of which are in the chamber. He claims that what most people don’t realize is their coordination of movement is deeply informed by subtle sounds, and removing them entirely means that some people have difficulties even walking.

“You take away the perceptual cues that allow you to balance and maneuver,” he said. “If you’re in there for half an hour, you have to be in a chair.”

Some companies have used the chamber to test various things, for example, Harley Davidson used it to chill out the engine noise on a recent model, while NASA has used it to help astronauts get accustomed to the vacuum of space.

It’s a rather unique attraction for those visiting the Minneapolis area, and a whole hour with up to four people in the chamber costs $400.