CaixaForum Madrid is a post-modern art gallery in the centre of Madrid. It is sponsored by the Catalan-Balearic bank La Caixa and located next to the Salón del Prado. Although the CaixaForum is a modern building, it also exhibits retrospectives of artists from earlier time periods and has evolved into one of the most visited museums in Madrid. It was constructed by the Swiss architects Herzog & de Meuron from 2001 to 2007, which combined an old unused industrial building and hollowed it out at the base and inside and placed on top further floors which are encased with rusted steel. Next to it is an art installation of green plants growing on the wall of the neighbouring house by French botanist Patrick Blanc. The red of the top floors with the green of the wall next to it form a contrast. The green is in reflection of the neighbouring Royal Botanical Gardens.