Float tanks also known as isolation tanks are becoming more and more popular in the USA and Canada because even though they are classified as an 'alternative medicine' they provide real results. Float tanks are small 'pods' just large enough for a grown adult to lay in without touching the walls. The tank is filled 3/4s of the way with a solution of filtered chlorinated water warmed to the same temperature of the skin and Epsom salts you lay in the water floating with the door closed blocking off all light and most sound. The salinity level of the water in the float tank is kept higher than the salinity level of the ocean, allowing the person the tank to easily float in the water and blocking out the feeling of gravity.
Once in the float tank most of your senses are deprived of any stimulus from the real world. You don't feel gravity, you don't hear anything you can't see anything, and you don't feel warm or cold. In this state your mind doesn't need to process as much information and is allowed to relax and wander. Some people liken the experience to dreaming while awake or meditation, or even similar a psychedelic experience. Most people who try float tanks, and even people who are skeptical of them enjoy the experience when they are given a chance to experience a float tank.
Usually people stay in the float tank for at least an hour because it takes some time before the mind really begins to relax and you get in the state of mind you are trying to reach by being in a float tank. You should get a good night sleep and use the bathroom and even shower as a preparation for entering the float tank.