After four weeks of travel and years of planning, the Silk River has reached the end of its journey with the closing ceremony today at Kolkata’s Victoria Memorial. It is hard to believe that two years have passed since I first met Ali in a sandwich shop on London’s Kings Cross station and she attempted to sketch out an idea she had had: to link, through the act of walking and the medium of art, the historic rivers of Hooghly and Thames. What drew my attention immediately, as a traveller and a writer, was the instantly recognisable fact that she was on to something with this riverine pairing. Both rivers are famous waterways, the Hooghly being the name for a section of the Ganges, both being conduits in their time for fabulous wealth that flowed from one to the other, and both in some ways forgotten.

There is something going on with the geography of Calcutta that I don’t understand. It ought to be simple. There is a city built around a straight river. There is a big bridge at one end and a big bridge at the other. The two bridges are very different: one soars gracefully, the other spans with brute force.

Ask any British person where in the world they would like to go, at least once in their life, and I’ll bet that a visit to India would be at the top of the list. And if there was one experience that such potential visitors would specify, it would be a journey on Indian railways. This morning we cross the Hooghly again and land near Howrah Station, a place that encapsulates all the excitement, energy and controlled chaos of Indian railways. It is the turreted temple of rail journeys.

It’s our last day on the river today. We leave at seven in a fast-running tide that’s carrying rafts of water hyacinth along, some of them inhabited by pond herons. You might think that as we approach Calcutta the wildlife might disappear, but as we pass under Howrah Bridge a dolphin surfaces to breathe and there’s a boat anchored nearby where fishermen are diving with face masks. I cannot imagine that they can see much. There are kingfishers here too, one is using a mooring rope as a lookout point.

After breakfast we take a bus through Barrackpore and get down near the river a few kilometres upstream from where we are staying. Then we walk down a small lane with walls on both sides. To the right is Mangal Pandey park and to the left – I peep over – there is a beautiful garden with wide tree-shaded lawns and a big house with a huge verandah. Among the trees is a tall tower that looks like an old lighthouse and, arranged around the lawns, several bronze statues on plinths. I’m intrigued. What is it? No one seems to know.

Dawn eases the world into view from the boat. We are anchored off Chandannagar where today there will be a parade. It’s the best yet. We walk down The Strand with drummers and a team of acrobats on stilts wearing peacock feather headdresses.

During the night, when we are chugging downriver from Krishnanagar, there is torrential rain. Visibility at dawn is not much better. It’s what the Scots call dreich: thicker than mist, but not quite rain. In the wheelhouse, our pilot Nimai, is working hard to steer around the sandbanks, many of them invisible to ordinary mortals. But he sees them.

I like a town with a speciality. Nuremberg is wooden toys, York is chocolate, Buenas Aires is tango and London is second-rate politicians – no, hang on, every capital city seems to specialise in those.

Just before dawn we are on the riverbank about to be ferried out to our boat which floats offshore in the pearly mist. The sky and the river are same shade of grey. For once the world is hushed and almost silent.

One wonderful thing that happens when you travel through a landscape with something of a purpose is the chance encounters, the unexpected conversations that suddenly open up unseen worlds. Like with Darshan last night in Azimganj when he let slip about the elephant.