They were inaugurated in 1996 on Plaza Castilla in Madrid. If you keep walking South you will get to the the Santiago Bernabéu, Real Madrid's stadium.
Even though the name of the towers is "Gate of Europe", they are better known as Kio Towers, since the development company was Kuwait Investments Office. They are the entrance to Madrid from the North.
But now they have great competitors: the huge Cuatro Torres Business Area, the new business district that has settled in the Paseo de la Castellana. The highest tower is 250 meters, the highest in Spain.