It appears on the map as 'Government Buildings'. When you find it, tucked away behind some residential housing, it does not bring to mind military installations on occupied corners of tropical islands. The razor wire and bars on the windows are your only clue that this is Colnbrook Immigration Removal Centre, the seemingly permanent location of Britain's indefinite detainees.
Unable to be deported, yet endlessly refused release, the detainees here watch planes take off and land at Heathrow airport through the thin strips of their cell windows, and they wait. As weeks turn into months and months turn into years, they wait.
Some cannot be deported because their country of origin is too dangerous - the courts have stopped the government deporting people to Zimbabwe or Somalia, for example.
Others are from countries that will not accept them back. Iran is actively seeking to stop asylum seekers being returned there, while the first attempted deportation to Baghdad late last year ended in embarrassing failure when the Iraqi military ordered the flight to leave immediately without allowing the Kurdish deportees to disembark.
Migrants from these countries are being left in the limbo of indefinite detention.
How can that happen? When proposals to detain suspects for 42 days under anti-terror laws faced such widespread condemnation, how can a young Somali called Mohammed be entering his third year of detention, waiting for an impossible deportation to the most dangerous city on earth?
Mohammed can't understand it. When I met him in February he told me how he used to love this country that had given him refuge: 'the way people express themselves, and freedom of speech, all these wonderful things'.
'Now I'm looking at another side of the system,' he said.
Mohammed came to the UK ten years ago. After a childhood spent witnessing murders and seeing corpses in the streets, he found adapting to life here difficult. He was given leave to remain for four years, but afterwards was refused and not allowed to work.
He struggled with alcohol and drug addiction, and spent several short spells in prison. When he was charged with using threatening language during an argument, his solicitor advised him to plead guilty as he would get a suspended sentence - but he ended up being given four months.
Two years later, he is still detained.
'My freedom has been taken away,' he says. 'It is one of the most important aspects of human life, your liberty. I am in a small room - every single day is the same. Killing time, that is what we are doing and time is not supposed to be killed. Time is all we have in life.
'I'm not getting younger. All I want is to live life and have a family and do the things that other people do.'
Britain is almost alone in practising indefinite detention. France, for example, has a maximum limit of 32 days. Last year NGOs united to oppose the EU Returns Directive planned to extend a time limit of 18 months across Europe. But Britain refuses to implement even this lengthy time cap.
A string of High Court rulings have found indefinite detention to be unlawful. And earlier this year, the Court of Appeal ruled that the UK Border Agency had unlawfully operated a secret policy of blanket detention of ex-offenders, regardless of their individual cases.
Sixty years ago, the political thinker Hannah Arendt, herself a refugee who had been interned more than once, pointed out the limitations of 'inalienable' human rights. In reality, as soon as refugees appeared who belonged to no government or political community, no authority would protect their rights.
She diagnosed a condition of 'rightlessness', where refugees can say what they like, but 'their freedom of opinion is a fool's freedom, for nothing they think matters anyhow'.
But whenever the rest of us recognise refugees as our neighbours and community members, what they think starts to matter.
This is why the Detained Lives campaign against indefinite detention will be travelling around the country this year. Ex-detainees, released after years in detention, will be discussing their experiences - and how solidarity can oppose the marginalisation that culminates in indefinite detention.
Mohammed won't be there, for the moment: he will be in his cell, dreaming of becoming a youth worker to help kids avoid his mistakes, and of one day returning to a peaceful Somalia to buy his patch of land by the beach. Most of all, he will be dreaming that one day 'this will finish and I will walk the streets as a free man.'
Jerome Phelps is the director of the London Detainee Support Group, www.ldsg.org.uk For more information on the Detained Lives campaign visit www.detainedlives.org