You are butt-naked in total darkness. Sopping wet and totally alone, the space you're in is so small that you can't stand. The only sound is the thud of your heart. You are a mewling human baby in a mechanical womb.
Life is stressful! If the person you're shopping for is anxious all the time, you might as well help them out with a gift that will let them chill out, if but for a little while.
Yesterday, while touring a new building on Microsoft's campus, I came across an anechoic chamber: A room designed to eliminate all noise from outside—and in. I spent about 5 minutes locked inside, and man is it freaky.