The sacred Ganges is so entrenched in India's psyche that Jawaharlal Nehru, the first Prime Minister called it the "River of India", eloquently equating its ever-changing yet constant presence with the convoluted story of India's civilisation and culture.
It rises in the Himalayas and reaches the Bay of Bengal 2500 kilometres later, but its mystique spreads beyond its banks, reaching into the consciousness of people throughout India as well as its vast diaspora.
Non-Indians too, are intrigued by the Ganges, and during previous trips we'd encountered the river at the source stream in the Himalayas, then at various points on the way to the holy city of Varanasi. Now, a chain of serendipitous connections allows us to see the last thousand kilometres of National Waterway 1 - the Ganga, Bhagirathi and Hooghly river system - from a luxury riverboat that takes us to Kolkata on the Bay of Bengal.
We're supposed to start at Varanasi, but low water levels and red tape mean we drive east into Bihar state where the RV Pandaw IV is waiting.
Ganges River dolphins break the water beside us, their distinctive long noses and stunted dorsal fins clearly visible as they curve out of the murky river.
These endangered dolphins are almost totally blind, using echolocation to feed and navigate. Pollution, dams and fishing are major threats to their survival, but later in the cruise as we near the dolphin sanctuary an informative speaker cites education and moves to improve the river's ecology as positive factors.
As we wend through a web of channels between sand islands, shingly banks and the distant true banks, I recognise storks and stilts, geese, ibis, and shelducks. The onboard naturalist points out blue bull and black buck antelope on the shore.
Though wildlife abounds, the river is surprisingly devoid of people. Initially there's hardly any river traffic, and the navigable channel is often separated from towns and villages on the banks by kilometres of sand and water.
Occasionally we see herds of buffaloes driven down to wallow. Simple cremations are regular sights, mourners standing around small pyres at the river's edge.
Sometimes we tie up at places that give an insight into how the Ganges influences life ashore. On the first stop we clamber up a five-metre bank to a prosperous village surrounded by flourishing crops, which seems safely perched above the water.
However, when the Ganges is swollen by snowmelt and monsoon rain, the river swirls right through the village.
Most people leave, returning after the monsoon to a land that has been replenished with fertile silt and is ready to sustain the age-old cycle of planting, tending and harvesting crops.
On another day we pass scores of ancient, low-slung boats crewed by tough, wiry men who dredge sand using nothing more than buckets slung on bamboo poles. Onshore it's unloaded by the bucketful into huge dusty piles where more manual workers load it on lumbering trucks that cart it away for use in cement.
From afar, such hard work seems almost picturesque, but the following day we see reality close-up at a vast brick-making area, where hundreds of chimneys spike upwards from an arid plain, staining the sky with black smoke.
Dusty men, women and sometimes children toil in harsh conditions, shovelling sand from deep pits, mixing it with water, carrying it out of the pit, then hand-shaping it into bricks, which are then baked in a gigantic earth furnace.
Many workers live in makeshift huts among the quarries, where everything - including the children who swarm around us - is covered in a thick layer of dust. Witnessing such appalling conditions is a sobering experience especially when we re-board the RV Pandaw to find yet another magnificent meal waiting.
We leave the Ganges proper and enter the serpentine feeder canal that takes us to the Bhagirathi and Hooghly Rivers in West Bengal. The narrow waterway twists through a lush, fertile landscape punctuated by palm trees, orchards, market gardens and rice paddies filled with flocks of egrets and stilts. It's a sudden contrast to the featureless expanses of the Ganges, and there's more human activity. Fishermen cast their nets, excited kids run beside us along the banks, women twist and bash the laundry, music blares from houses and temples.
We stop at pleasant, shady villages where residents weave cotton cloth, make brass, roll bidis (Indian cigarettes) and farm. These simple, friendly places have active temples and shrines, but in sleepy Barannagar we're enchanted by an exquisite collection of miniature temples dating from the mid-18th century.
More striking temples are revealed at ramshackle Kalna, some of which remind me of Russian religious architecture, with steeply sloping roofs and layers of turrets and domes.
Kalna's most astonishing site is, however, the 18th century 108 Shiv Mandirs, or 108 Temples. This consists of two concentric circles of joined temples, the outer of which has 74 small, elegant temples, while the inner circle has thirty-four.
We stop at several mosques, including the cannon-scarred ruins of Katra Mosque at Murshidabad and the Hooghly Imambara, an active place of worship, schooling and pilgrimage for Shia Muslims.
Buddhism provides one of the highlights - a visit to the town of Bodh Gaya and its Unesco World Heritage site, the Mahabodhi Temple Complex - Buddhism's most important site. This is where the Buddha attained enlightenment circa 500BC. Today temples and monasteries cluster around the main temple, reflecting different countries' distinctive architectural and decorative styles.
At the Mahabodhi Temple we queue to see the seated golden Buddha within, but it's the surroundings I find most interesting. Tens of thousands of marigolds are arranged in elaborate patterns throughout the grounds, where pilgrims prostrate themselves towards the temple and the sacred tree - known as the Bodhi Tree - behind the temple. The tree shades the actual spot where the Buddha meditated and gained enlightenment, and young monks excitedly catch and clutch precious leaves that spin to the ground.
As we near Kolkata, sites associated with colonial history slide by. We enter the city at night, slipping beneath the illuminated spans of the Howrah Bridge and dropping anchor in the middle of the river.
It's the eve of Holi, India's exuberant Festival of Colours, and after dinner we're invited on the sundeck to "play holi", throwing away our inhibitions and following the energetic Bollywood moves of our young crew.
The music cuts through the humid air, pounding across the water to the twinkling lights of the once-grand colonial city, which waits to give us one last experience on the River of India.
Getting there: Singapore Airlines has flights to all Indian gateway cities, including Kolkata and Delhi.
Further information: In India, reputable company Assam Bengal Navigation offers cruise options that cover most places mentioned in the article. Otherwise, sites can be reached by rail, road and/or air.
The writer travelled with assistance from Pandaw Cruises and Singapore Airlines.