Most urban areas have one - an area that is a sort of no-man's land where no-one lives and which becomes ever more rundown.
In Cairo this was the case of the land adjoining the Darb al-Ahmar district. For almost a millennium assorted dust, debris and rubbish was piled up along the eastern rim of Cairo's medieval city walls.
Even though it lies close to the popular sites of medieval Cairo, the area was off the tourist track, blighted by prowling drug dealers and stranded between the Salah Salim highway and the City of the Dead.
But thanks to a $45m seven-year project by the Aga Khan Development Network, the dumping ground has been transformed into al-Azhar Park - North Africa's largest urban green space.
Part of the city wall built by Salah al-Din has been uncovered and the adjoining slum has been given a new lease of life.
For more than four years the whole place teemed with workmen in hard hats busy removing the topsoil, digging massive holes, laying foundations and bringing in plants, trees and shrubs from around Egypt.
The scale of the noise and dust caused by the work was almost overwhelming - but turning 30 barren hectares of the Darassa Hills into a lush, green park overlooking Cairo's Islamic city was never going to be easy.
The dream became a reality just a few weeks ago when the first group of Egyptians paid their entrance fee and entered a landscaped and well tended park.
"For Cairo to have this large patch of green is really marvellous," said one of the local residents.
"I am sure it will make a huge difference to the lives of everyone who lives nearby."
But it is not just the people who live locally who will benefit.
The park is on three major bus and tram routes and is quickly and easily accessible from other parts of the city.
The statistics are staggering. More than 250 royal palms have been planted with another 100 date palms.
There are 30,000 sq m of grass. Then there's a citrus orchard with mango, orange and lemon trees.
It's incredible to see my district changing so rapidly... Because people are involved in the work, they'll take care of it
Darb al-Ahmar resident
Overall there are 300 plant types and thousands of examples fill the park with colour and fragrance. But that is just the beginning. When the excavating was going on more than a kilometre of historic wall was uncovered that has lain neglected for almost 1,000 years.
That in turn led to another task - giving a new face to the historic part of Cairo as seen from the park.
This did not just entail a coat of paint, but the economic, physical and social upgrading of the neighbouring district.
The guiding principle of the multi-faceted project is to improve the quality of life of local communities.
According to Mohammed al-Mikawi who is project manager for the Aga Khan Trust for Culture in Egypt, the process of improving the whole district has provided a clear insight into the full array of contemporary development problems.
"It makes us question how best to connect an age-old heritage with the opportunities and demands of a rapidly changing modern life," he explains.
The Darb al-Ahmar district, its narrow alleys lined with teetering shacks and strewn with rubbish was once seen as a disreputable slum.
But now its 250,000 inhabitants are fully involved in the idea of upgrading their own area.
Some of the men have been hard at work providing the doors, window frames, and furniture needed by the new community centre, school and hotel.
Neighbourhood workshops that make ceramic tiles, carve wooden mouldings, or forge metal door frames are doing a booming business, supplying materials the community needs to rebuild.
This project has allowed us to save the urban fabric of this historic neighbourhood. More important, we are creating jobs and giving the people a decent future - Mohamed al-Mikawi
The workmen have been trained in their various crafts by experts, and their tiny shops now boast modern machinery. There are micro-credit programmes, vocational training classes, and even a new local choir.
"It's incredible to see my district changing so rapidly," says Naila who has learnt has to restore carvings on wood.
"Because people are involved in the actual work, I think they'll take care of the place. I don't think it'll go back to what it once was, if the Aga Khan pulls out."
With an official launch of the project planned for next year, there's still work going on to finish to cafeteria and five-star restaurant.
"This project has allowed us to save the urban fabric of this historic neighbourhood," says Mr Mikawi.
"More important, we are creating jobs and giving the people a decent future."
It's the kind of holistic, costly and complicated project that experts say the world needs many more of.