Puerta de Europa is a major office and residential project which stands astride the paseo de la Castellana, Madrid’s most important boulevard, on the north side of the Plaza de Castilla. These twin towers are the world's first leaning high-rise buildings.

The location of the site over a subway interchange makes it structurally impossible for the buildings to stand near the street. In order for the two towers to read as a pair, they were designed to lean toward each other over their plazas. This bold move creates a portal which, being at the northern end of the business district, becomes the gateway to Europe, hence the name of the project.