Hear that faint buzz? There's a secret society in Pittsburgh this week, a minuscule group being initiated into the delicious "El Eco de la Sombra" ("Echo of the Shadow"), staged by Teatro de los Sentidos (Theater of the Senses) from Barcelona.

It comes as a gift of the Cultural Trust's Pittsburgh International Festival of Firsts, its generosity compromised only by the sad fact that it necessarily allows so few to participate -- some 50 each night.

The site is an empty armory in Shadyside, owned by Ellis School, where the company has built an intricate maze of draperies, dim lights and ingenious set pieces.

It's a solitary experience, but you are not alone. You enter through a dusty bookshop, where a soft-spoken, knowing clerk invites you to study the books, then beckons you forward, providing you with a slim volume that purports to be your own story and that is your passport to the experiences that follow.

You proceed from one mysterious encounter to another, sometimes bending low, sometimes winding down narrow, twisting fabric corridors in complete darkness until you turn a corner and head toward a faint light in another magical room. You go barefoot, you're read to, you lie down, you cross water, and a couple of the encounters are so extraordinary that ...

But I've said too much already, because if you are so lucky as to have tickets on the four remaining evenings, you don't want to know in advance what to expect. All you need is trust. This is no haunted house, stocked with shock. Instead, its softly eccentric inhabitants guide you subtly though a dream-like experience that is a cross between sensory therapy and some not-so-Grimm middle European fairy tale.

All the five senses are stimulated. I imagine what you get out of it depends a lot on what you bring with you. I emerged as peaceful as I can recently remember being. Not even talk of the presidential campaign or the Red Sox loss to the Rays could shake my heightened calm.

Doubtless, although tightly scripted and organized as the experience must be, each participant will encounter it differently. Half the fun is talking about it in the days ahead with fellow initiates -- there ought to be some visible symbol we could wear, so we could identify each other on the street.

Through Saturday, 7-11 p.m.; www.pifof.org or 412-456-6666.