Little children playing naked in pools of viscous water; rows upon rows of rusty tin shacks, implausibly teeming with human life; a man in the crowd wearing an Arsenal shirt.
These are some of the images that catch the eye as you drive through the labyrinthine alleyways of Majengo, Nairobi's giant slum.
But it is the shoes that linger. Thousands upon thousands of shoes, piles of them for sale on rickety market stalls -- on every corner, more piles.
It is a puzzling spectacle. A nurse riding with me in a minibus packed with medical workers offered a compelling interpretation. They are dead people's shoes. "People who have died of AIDS."
People compare the AIDS disaster in Africa with the 14th-century plague in Europe, but here is an image recalling a more recent horror, the shoe mountains which Allied soldiers found in the Nazi extermination camps. Except that the African holocaust continues, under our noses, at a searing pace; except it is impossible to claim ignorance of what is going on.
The statistics have been recited so often they deaden the mind. But, at a time when the resources of the rich countries of the world are focused on what are, in numerical terms, the relatively innocuous consequences of terrorism, one should force oneself to pay attention.
To reflect on the fact that 7,000 people die of AIDS each day in Africa, that 17 million have died since the disease first appeared two decades ago, that more than 30 million Africans are living with HIV/AIDS, most without access to the anti-retroviral drugs that have contained the disease in the US and Western Europe.
Here in Kenya, in a continent synonymous with catastrophe, there is some good news on what ought to be the great cause of our time, a cure for AIDS. Barely six months ago Kenya emerged from 40 years of corrupt single-party rule to initiate a new era of democracy. The US and Britain's chief concern here is that al-Qaeda operatives may be hiding out on Kenyan soil. For Kenyans, the big issue is an enemy that has orphaned 1,250,000 of its children.
Majengo is the main battleground and a woman called Agatha is on the front line.
Her life is sordid beyond imagination. A prostitute who works out of one of Majengo's tin shacks, smaller than a double bed, she makes an unlikely medical heroine. Agatha is 52 and a grandmother, but still has sex -- when she is lucky, she says -- with 40 clients a day. What makes her even more remarkable is that, in tests systematically conducted over two decades, she has never tested positive for HIV.
She is one of a group of 50 prostitutes from Majengo who have demonstrated a resistance to an illness that has killed many of their clients and killed off 95 per cent of the female competition.
Studied by researchers from the University of Nairobi and the University of Oxford, they were all found to have an inordinate quantity of white blood cells perfectly honed to kill HIV-infected cells. The information obtained from the women has been converted in laboratories at Nairobi University's Faculty of Medicine into a trial vaccine. The first tests on humans began this year. No other project in the world is more advanced or offers more hope that the holy grail, a lasting solution to AIDS, may be found.
Africa, always the problem, could turn out to be a large part of the solution. It is symbolic of Kenya's new determination to achieve political health that Africans are doing it for themselves. In the ground-breaking research they are providing not just the 50 miracle women but also the scientific expertise.