Sensory-deprivation chamber.

Inside the tank. (David Senior illustration, For The Baltimore Sun / January 11, 2014)

Featured in SceneOn the second day of the year, I stood naked above the tank of water saturated with Epsom salts, preparing to close myself into total darkness.

In less than an hour, I would find myself in a drug-free altered state, feeling my body melt into the warmth and interviewing a vision of a woman playing the piano.

I was in the home of artists and musicians Twig Harper and Carly Ptak, a West Baltimore rowhouse with shelves stacked high with books about the occult and psychology and a 9-foot-tall statue of a Yeti-like creature.

Harper had purchased and constructed the sensory deprivation tank, called a Samadhi Tank after the Hindu word for a higher state of awareness, in the spring. Since then, he has started a therapeutic spa of sorts called Be Free Floating, renting out 60- or 90-minute "floats."

With his curly hair and bright blue eyes, Harper could pass for the low-key kid brother of Gene Wilder's Willy Wonka. The couple's cats, Binkie and Pipsqueak, drowsed in armchairs while he propped his legs on a wood stove and explained that he decided to experiment with sensory deprivation because he's long had "a passion for altered states of consciousness."

"The tank is the safest and most reliable way to go into an altered state," he said.

John C. Lilly, a neuroscientist and psychiatrist whose interests included dolphin-human communication and psychedelic drugs, invented the isolation, or sensory deprivation, tank in 1954 as a channel for people to reach a deeper state of consciousness.

The phenomenon has grown more popular in recent years. Locally, flotation spas have popped up in Bethesda and Manassas, Va.

The tanks are lightproof, and heaters keep the water and air at skin temperature, around 95 degrees. The high concentration of Epsom salts makes floating effortless, so that the water cradles your body, relaxing your spine and limbs. There are few sounds — I could hear not only my breath but also my pulse.

Floating in the tank induces a deep state of relaxation, soothes aches and tension, and eases sleep problems, according to Lilly's writings and the tank's manufacturer.

But the most fascinating aspect of using the tank is experiencing how the brain amuses itself when there is little or nothing to see, hear and feel.

"If you don't have sensory input, you start hallucinating," said Johns Hopkins University neuroscience professor Hey-Kyoung Lee. When neurons don't receive information from the senses, the brain focuses more attention on the impulses shared between neurons, giving rise to hallucinations.

Proponents of sensory deprivation say that in the tank, the mind slips into the dreamy state one experiences when falling asleep or waking up.

This lucid dreaming can be used to meditate, explore thoughts and feelings, or solve problems. One computer programmer sprang out of Be Free Floating with the solution to a puzzle that had long troubled him, Harper said.

I bought a package of three floats for $100. For the first one, Harper said, your primary goal should be growing accustomed to the tank and the experience of being in warm darkness.

He assuaged any fears I had about the cleanliness of the tank. The high concentration of Epsom salts kills microbes, and the water is further purified with ozone between floats. Clients are instructed to shower before using the tank.

I did the first float shortly before Christmas, sandwiched between interviews on a busy reporting day. The tank room is a soothing place, warmed by heated panels and illuminated by colored lighting that can be adjusted with a remote control.

The tank looks vaguely like something out of "Doctor Who." The hatch is lightweight and lifted easily, revealing a shallow pool encased in black walls. I crawled in.

I was instantly struck by an intense sense of buoyancy. It took force to touch the bottom with my hand or foot, although it was easy to move my whole body to sit up.

If you've ever soaked an infected finger in a cup of hot water with Epsom salts, you know that it can sting. So, with my parched winter skin, I felt a bit like a giant sore thumb, but the sensation soon faded.