I leave these notes for whoever may find them. I would ask you to turn back, but if you're reading this, I know you won't.

I first encountered them in 1996. I was fresh out of college then, with my pockets full of lint and little else to my name. I found shelter wherever I could. A friend's garage when their family was out of town, an abandoned flower shop with a false floor, the back of a van, anything worked for me. I was young and scrappy then; I thought nothing of it.

I bounced between homes, and even sometimes houses, for the better part of a year before I found my footing. Whether it was luck or the law of large numbers, I'll never know, but I found a place to stay. The landlord didn't ask any questions and the rent was cheap--cheap enough to warrant overlooking the lack of basic utilities, at any rate. I had lived without a roof. I could survive without running water.

Odd jobs gave way to a steady income, and hardship to routine. It was the summer of 1996, a hot summer, amplified by the concrete walls and my own restlessness. Sweltering. Endless, I sometimes thought--that was when I first encountered them.

I heard it before I felt it: a whisper, a cold caress on my left cheek. A draft. In a locked room, in the middle of summer. I'm a curious sort. Sometimes you have to be. Those four walls had been as familiar to me as my own body until then; now something new presented itself, so I followed it.

I knew I was on the right track when I placed my hand to the wall opposite to the door. My fingers ran through the familiar mortar until something drew my attention. There was a hairline fault in the wall, and as I touched it, I could feel the wall slide into itself.

Beyond lay darkness. Winding, awful darkness, howling like a set of windpipes recently unblocked. I didn't welcome the cold; it was heavy, it was thick with must and rot, and it clung to my skin and my clothes and my bones.

My landlord stopped answering my calls. I doubt he could have fathomed the enormity of what I'd come across--then again, back then, neither did I. I tried to explore the passage on my own, but as soon as the first footfall echoed through the twisted halls, I knew there was nothing there for me but disaster. Bones crunched underfoot. Just rats, I told myself, nothing but rats. It made me nauseous to imagine that I'd been sleeping and eating and washing just inches from this filth, but it still felt more comforting than the alternative.

When the path's first split presented itself, I knew I was in over my head. When I turned, I thought I saw the path shift--a telltale sign of the place getting to me.

I moved out by the end of the month. Another wall had collapsed, revealing another entrance to the catacombs, and my landlord's silence became too much to bear. I suspected foul play--at least, that's what I would have told anyone that asked. In truth, I was afraid. Afraid the woodwind tune would become a siren song.

That was the first time I encountered them. It was not the last.

Winter of '98. The snow on the driveway falls into a sinkhole--a perfectly rectangular one. A breeze whistles a familiar tune.

Council housing, '01. I have been to my basement hundreds of times, but that night, when I open the door, I find something else on the other side.

I begin seeing it in my dreams. I examine every wall, peek behind every painting. Walls lined with alcoves. Winding paths paved with bones. Not rat bones. Not anymore. The breeze fills me with panic. I'm tired. So tired, all the time.

The earth under our feet breathes. We were never meant to notice it, but put your ear to the ground for long enough, and you'll begin to hear it. The thrum. The catacombs, the veins and arteries of the land, reaching out, breaching through, closing in. Wherever we invite them in, they meet us. Whenever we call out, they answer.

You know this, don't you? You're here, reading these words. From the moment you stepped into these galleries, you have known this, whether or not you realise it. In this, we are siblings.

I would ask you to turn back, but I didn't, either. The woodwinds sang my name. They have been doing it since before I was born.

My only choice was to listen.