An immutable bridge

''Tomorrow,'' said my sister, ''we'll go to Hawk's Nest.''

It was, for a seven-year-old, the dream of a lifetime. She was twice my age; and for years, it seemed, I had heard about Hawk's Nest. Not that I was sure just what it was. I knew only that it was way out in the woods, and had to do with a river and some sand. I knew that it was a long walk from our house, and that it was positively the most wonderful place you could imagine. I knew that its name was shrouded in mystery - that it had nothing to do with either hawks or nests. And, of course, I knew that it was ''secret'' -- a word which, more than any amount of mere description, assured me of its desirability.

I had come of age to share the secret. So I was feeling particularly grown up when we set out early, lunch bags in hand, into the fine June morning. We followed the railroad tracks for the first mile, then turned down Strong Street, cut through the woods, and came to a field. Some distance away stood a farmhouse.

''Sh!'' said my sister, holding open the strands of barbed wire for me to climb through. ''Crouch down!''

Stooping over, Indian-fashion, she ran across the crest of the hill and disappeared through the far fence. I followed, obediently bent double -- though I recall wondering why. The farmhouse commanded a full view of us however we went.

But our game seemed to work. No one yelled at us, and pretty soon we were walking briskly along North East Street, our jackets tied around our waists, talking of this and that. On our left were more fields. On the right, cow pastures sloped gently down to a border of trees a long ways back. Beyond them, faintly blue in the distance, rose the Pelham Hills.

After a while my sister slowed the pace, looked furtively around -- though by now the nearest house was almost out of hailing -- and suddenly darted into a narrow dirt road on the right. I followed. The track ran flat beside pines, planted some years back in rows, and finally emerged in a kind of gravelly turnaround.

''The rifle range,'' she whispered, pointing ahead of us.

I could see nothing but trees. But she soon found a sandy path running through the slowly warming underbrush. We were coming up over a little rise when she grabbed my arm. There, two steps ahead, the brush stopped abruptly at a ten-foot ditch.It was lined with concrete. Looking over the edge, I saw great rusted contraptions of gears and levers.

''For targets,'' she said, ''from the war. See?''

And stooping down, she plucked a spent cartridge from the sand and handed it to me.

I was astonished. I knew vaguely about the war, knew that my best friend's dad kept a brown Army hat on the top of a glass-doored cupboard in his living room. And as a boy whose backyard often doubled as the Wild West, I knew a Colt from a Winchester. But here, somehow, was a touch of the real thing. Here was a place in which the imagination could have run wild. Here we could have played for hours with pine-branch rifles, taking trench after trench from fierce enemies battling among the old machinery.

''So this is Hawk's Nest,'' I breathed.

My sister paused, then laughed.

''No, dummy, this is the rifle range. Hawk's Nest is over here.''

More scrub. More barbed wire. A marshy meadow, the mid-morning sun by now hot and strong, and wet shoes. Then a strangely open forest, with no underbrush but with odd sweeps of gravel and logs scattered about where the river, in its spring flood, had put them. And finally the river itself -- a wide stream, really, gurgling over glossy red-brown stones.

We followed it downstream for a ways, and came around a bend. My sister stopped.

''There it is,'' she said.

I found myself looking at a wide, vast bank of sand on the far side of the river -- more sand, it seemed, than I had ever seen. Its toes stood in the water, from which it angled steeply upward. And far above, higher than the steeple of the church near our house, was its head, a vertical wall of hard sand overhung with a thatch of sod like the forelock of a giant. Growing from its top were the ever-present pines.

I have never been able to explain why, in the hours that followed, I was so awed. I had seen sand before. I had eaten lunches in the woods. I had even stripped to my underwear and plunged into streams before, coming out screaming to dance and shiver on a fallen tree trunk until the sun and my motion dried me.

Nor was it simply the exhilaration of our antics in the sand. We would race each other, orangutan-like, to the top, using hands and feet to scramble through the soft and sliding sand. In the shadow of the top wall, beneath the cliff swallows' holes, we rested, looking down on the treetops across the sun-sparkled stream. Then suddenly we would spring outward in tremendous kangaroo leaps, bounding in great arcs down the slope to the river. Up and down we went, over and over, until the afternoon sun wore away and we had to leave for home.

No, it was not simply my newness to the place that created its special aura. In the years that followed, I returned many times, and the specialness never waned. Part of it, no doubt, was in its remoteness. Had it been closer, or accessible by car, it would have lost that feeling of a goal hard won. And part of it was the sense of responsibility demanded by that very distance -- the grown-up seriousness of spending a whole day away from home.

But as I think back on it, I see that the true specialness of Hawk's Nest lay in its capacity to be nothing but itself. We never seemed to play at anything there -- never pretended it was a mountain full of enemy soldiers, or the river a raging Yukon torrent full of grizzly bears, or the fallen log that bridged it a ship full of buccaneers.

It was enough, somehow, that it was Hawk's Nest -- unpretentious, isolated, a separate reality in a world full of fantasies, a bridge out of childhood into adulthood. It was itself. So, for me, it has always remained.