By Selma Chalabi
Presenter, Kala Pani: A Forgotten History
Cellular Jail is shaped like a bicycle wheel - this is one of its 'spokes'
When I listened to my grandfather's stories of his time as governor of the Andaman Islands, it was the first I had heard of the jail where India's most prominent political prisoners suffered at the hands of their British colonial rulers.
It was strange, listening to the voice of my grandfather telling his life story after he had died.
But this was how I came to discover the part he played in Britain's dark history on a group of tropical islands located in the Bay of Bengal.
After the first war of independence in India in 1856, the Andaman Islands were identified as an ideal place for British colonial rulers to get rid of unsavoury elements.
Where better to put people you no longer want around but can't kill, than on some distant islands 1,000km away from the Indian coast?
Visitors to the islands may not be aware of their dark history
I learned that my grandfather, Noel Kennedy Paterson - NKP as he was affectionately known - was linked to this far-flung place a few years after his death, when my mother told me about a box of cassette tapes featuring his voice.
It was his last three tapes that caught my attention.
Labelled Andaman Islands 1, 2 and 3, I bypassed all the others and immediately got caught up in the story of this distant outpost of Britain's Empire.
'Worse than death'
For 20 years NKP was a member of the Indian Civil Service, in which he rose from the ranks of District Officer in the Central Provinces to Chief Commissioner of the Andaman and Nicobar Islands.
Known to Indians as Kala Pani - which literally translates from Hindi as Black Water - these islands represented exile, alienation, isolation and oppression.
Crossing the black water was not only about being far away from home - it meant that you lost your caste.
It's hard to imagine what that means as Britain doesn't have a similar social system, but it's far more than class.
It embodies religion, political power, occupation and identity. To lose one's caste is akin to being thrown out of the tribe.
In later life, NKP fought tirelessly for compensation for the prisoners
For a particular type of prisoner, being sentenced to imprisonment on the Andaman Islands was a fate worse than death.
My grandfather briefly referred to the political prisoners as terrorists, but skirted around the issue.
It was this evasion that sparked my curiosity. I wanted to know who these people were, what happened to them, and what they represent now.
While Gandhi and his non-violent approach to British rule is well documented, there is less known about a highly organised armed struggle prior to, and overlapping with, Gandhi's movement.
People involved in conspiracy cases, armed robbery and attempted assassination plots were sent to this jail in the islands' capital, Port Blair, and kept in solitary confinement.
Known as the Cellular Jail, there were almost 700 single cells in total, each measuring 4.5m by 2.7m.
The aim, according to hobby historian Francis Xavier Neelam, was to "break the spirit of the freedom fighters".
"Crossing the black waters was a double penalty. It meant you lost whatever status you enjoyed on the mainland, as well as facing torture and isolation."
I was fortunate enough to meet the last surviving political prisoner sent to the Cellular Jail.
Sri Bimal Bhowmik, sentenced in 1934 for possession of firearms, was held in solitary confinement and, like many of his counterparts, was made to walk around in circles for hours grinding coconuts into oil.
Work like this was usually carried out in villages by oxen. If you didn't fulfil your quota of oil, you might be whipped or held in bar fetters - leg irons that restricted your movements.
"We knew about Kala Pani, or Black Water, which one had had to cross to reach this destination.
"The water wasn't really dark; it was the notion of this place. When we reached there, we knew that would be the end - a point of no return."
In fact, Sri Bhowmik did return from Kala Pani. In 1937, many of the political prisoners held in the jail went on hunger strike, and their plight chimed with the times.
India was on its way to independence, and the terrorists or freedom fighters - depending on the view of their struggle - were repatriated.
When my grandfather arrived on the island in 1938, nearly all the political prisoners had returned to mainland India.
Cellular Jail contains almost 700 solitary confinement cells in total
What he inherited was a curious experiment in penal reform - where many of the criminals were murderers and thieves brought in to fulfil the labour force that was needed.
By the time my grandfather left India in 1947, he was answering to India's new masters, people like Nehru and Home Minister Patel.
For me, this programme was an opportunity to delve into a darker, hidden part of our history. As its erasure from our history books indicates, it's a part we would rather not know about.
Now a holiday destination, British people visit the islands for their perfect palm-fringed beaches and spectacular diving sites.
But before heading straight for the beach, perhaps they should follow the lead of Indian tourists who, in a spirit of pilgrimage, visit the Cellular Jail in Port Blair.
It was here, after all, that hundreds, if not thousands, of young men languished under British rule.
Young intellectuals, journalists, and men like Sri Bhimal Bhowmik - who believed that the only way to achieve independence was to take up arms against the British - and who ultimately paid the price by crossing Kala Pani.
Kala Pani: A Forgotten History can be heard on BBC Radio 4 on Wednesday 21 April at 1100 BST and afterwards on