On a dry hillside near Madrid, a black mass has taken over: stacks of discarded tyres, piling up for years in an environmental nightmare for the small town nearby.
"The visual impact is dreadful. The countryside is totally spoiled by this black mark," said Vicente Garcia de Paredes, an activist with environmental group Ecologists in Action.
"This is an area of great views. Drivers on the highway to Andalucia will have this view stuck in their minds."
The massive pile started to form in the 1990s when a company began using the site as a temporary depot for old tyres due to be recycled, according to the mayor of Sesena, Carlos Velazquez, who inherited the problem when he was elected in 2011.
But over the years the tyres started to pile up. Millions of them lie there, in a wild dump stretching over 10 hectares (25 acres), home to rabbits and secured by a sole security guard at the fence.
The tyres are of all sizes. The majority come from cars. Larger ones come from trucks. Some are still in good shape, others unusable.
Environmentalists warn that disease-bearing mosquitos may breed in the stagnant puddles that have formed in the hollows of the tyres.
The town of Sesena lives in fear of the rubber heap catching fire.
"The dump was formed bit by bit. The company did not have a licence to leave the tyres there indefinitely, but that's what ended up happening," said Velazquez.
"Tyres were being brought here but no tyres were leaving, so a dump developed," he says.
"If it caught fire it would be very difficult to put out."
After the dump was declared illegal in 2003, the company that ran it was chased through the courts and it eventually abandoned the location.
In 2010 a judge ruled that the tyres were abandoned waste and the council was responsible for clearing them.
Environmental group Ecologists in Action estimates between 40,000 and 60,000 tonnes of tyres lie in the dump—regular car tyres and chunky ones from heavy trucks.
"We are less than five hundred metres from a town of 10,000 inhabitants and the material is dangerously flammable," says Vicente Garcia de Paredes, an activist from the group.
He points down the hillside to the brown ranks of housing blocks on the edge of town.
Developers built those during Spain's building boom from the late 1990s, hoping to draw tens of thousands of people to buy homes there.
Now Sesena has become a near ghost town, a symbol of Spain's economic fall since the boom went bust in 2008.
The town hall has at last signed a deal with a company based in Senegal that will spend three years milling down the tyres and trucking the bits off for recycling, said Velazquez.
The company will use a machine to grind the tyres on the site and then ship the pieces by truck to recycling centres.
The tyres are likely to be turned into building materials: surfacing for roads, sports tracks and children's playgrounds.
The site is due to be cleared within three years.
Explore further: The Great Barrier Reef should not be listed as 'in danger'