The directions I’m following were detailed, but unconventional for a London address: “A river; a winding path; a gate; an apple tree; a reedbed; a plank … Stay on the left as it’s wobbly.” What my friend Paul Powlesland didn’t say is that the plank would feel like a modern day Sweet Track, a walkway raised above the tidal marsh into another world. Arriving after midnight at his mooring on London’s neglected third river, the Roding, I find myself in a susurrating darkness that almost subsumes the late-night traffic noise. Paul didn’t say, either, that the final section of plank would be slimy with rain and listing precariously above the water. But I make it, and install myself in his floating yurt, where I’m spending the night. London is out there, not muted, but blurred into a saltmarsh soundscape. The sense of being surrounded calls to my drowsy mind a line in Maurice Sendak’s Where the Wild Things Are: “That night … the walls became the world all around.” I wake to bright sunshine and a blast of Cetti’s warbler song – as loud and assertive as the wren I hear at home, but sharper, and without churring trills. The yurt door opens on to a wall of whispering green. Over the reedheads I can see the breeze-ruffled tops of aspen, willow and cherry trees, two tower blocks, and a crane. The world really is all around. I start to explore the thatch of vegetation along the riverside path – an eclectic mix including nettle, bramble, yarrow, teasel, black horehound, oxtongue, goat’s rue, fennel and dream-inducing mugwort, whose nicknames include river wormwood (apt) and naughty man (intriguing). Among the reeds, naughtier still, are the deadly umbels and fronds of hemlock water dropwort. The diversity is unexpected, but not accidental. Paul is a co-founder of the Lawyers for Nature collective and the founder of the River Roding Trust, and his activism never sleeps. He points out several smaller trees, hidden in the botanical throng. “The Trust took on this scrap of land for nature restoration. “This is not a wealthy neighbourhood, but nature is for everyone. The plan is to have one of every British native tree here so anyone can come and meet them.” The reeds applaud, softly.