" The landfill has been servicing Barcelona's metropolitan area for over 30 years. More than 20 million tons of rubbish was spread around the valley before the site was closed in 2006. In some places, you would have to dig down over 100 meters before you found soil again.
But this isn't just a cosmetic makeover. There is an underground drainage system on site which filters contaminated waste fluids. Part of this recycled water is then used to irrigate the park. 'The whole project is very sustainable,' [architect Joan] Roig said.
Furthermore, the dump is also utilizing the bio gas that is emitted to provide electricity.
Some of the rubbish has remained above ground. Housed in large steel cages which flank the entrance to the site, Roig says they serve as a permanent reminder to visitors of the site's previous life."