The secret garden

Along the northern edge of the floating harbour there used to be, when I visited the city in the 1970s, a corridor of benign dereliction. The harbour wall was intact, there was a walkable path above that, but between the path and the main road lay an area of disused and overgrown industrial wasteland. It was a long finger of regained ecology, a domain of character and natural misrule, pointing from the basin (where it was narrow but vital), past full expression around the disused docks, to the centre of the city. Wildlife thrived there; courting couples drifted there; people came from their offices to sit in the peace and quiet while eating their sandwiches away from the hubbub.

Then redevelopment set in. It gained a first foot hold twenty five years or so ago at the cityward eastern end, with establishment of the media centre. It's crept inexorably down the dock line to the west ever since. The water's edge path was the first strategic defeat: an exuberantly anarchic coëxistence between traveller and environment became a sober, polite, carefully ordered sterile copy of a suburban street. The hinterland was still there, but the path was the writing on the wall.

It took time for the whole area to succumb. There were a couple of decades during which progress was almost imperceptibly incremental, always from the cityward end and always along the waterfront. Then a rash of car parks covered the docks area from the landward side. A new square, a science centre, a bank headquarters, an acne of offices, pubs and a nightclub, erupted near by. The water edge path ceased to be separate, becoming absorbed into the newly paved public spaces.

After that the infection leapt to a second focus at the far end. Gentrification, spilling down the hill from old money area on the hill and along from the basin, spawned a fungal growth of expensive upmarket flats. These flats were designed with vaguely nautical touches such as the odd circular port hole window. They, too, transformed the water edge: the path, here, became a patio extension faintly reminiscent of an aircraft carrier's service deck.

It didn't then take long for the green core of the area to succumb. The expense of cleaning up industrial ground contamination while simultaneously preserving at least the shell of industrial architecture was all that had protected it for so long. With expensive development on either side, rising values at last made it irresistibly economic. In came the unintentionally ironic slogan "Building a soul in the heart of the city".

The work is not yet complete, but all trace of what used to be has gone beyond recall. Much of what is being built is a light and airy environment, well designed and pleasant, but not in any way unique. It's a cleaner, in many ways better, place – but not a place to play, or to sit, and loss of the old wild wood magic is the price paid for it.

In places, though, fragments of the old riotous chaos and rich decay still hold out in secret invisible corners. They are, for the most part, along the water margin and at water level – out of sight from the serious and well mannered walkway, but nestled in a variety of ways between it and the water itself. Here, a long tunnel of green; there, a hidden string of brackish pools swimming with life; somewhere else, a disused flight of steps – built over but dry, colonised, and still discoverable from water level. People with cameras can regularly be seen peering over the railings (railings!!!) to cautiously photograph the marginal fringes, but I've never seen anyone else scramble down over the edge and explore what lies behind them. No, I'm not going to give you details; if you're serious about them you'll find them for yourself; if you're just a tourist they can stay undisturbed.

This morning I went down to the path and (after waiting a minute or two until there was nobody to see) swung down into one of these microworlds. The city disappeared. The voices of passers by along the walkway were still there, but disembodied and unreal. The traffic noise was gone completely. Watery sounds predominated, with an overlayer of boats and bird calls. Continuity is very limited; after a hundred metres of one habitat, there was no way to continue without swimming, so it was back onto the asphalt until I could drop back into the next little primeval island.

Eden isn't all sweetness and light, of course, especially in retreat before industrial urbanisation. There is a mange of weathered plastic and other human detritus intertwined with the unrestrained natural growth. On one tangled stretch of outgrowth I had to step over an abandoned swans' nest; seven huge, undamaged but unhatched eggs were scattered sadly across the unravelling circle.