If you are a fan modern architecture, do not forget to check out these twin towers, one of the tallest buildings in Spain. Also known as KIO Towers, they were designed by Philip Johnson and John Burgee.
The towers should represent the decline of traditional "right angles" and boredom in architecture.
Wikipedia https://en.wikipedia.org/wiki/Gate_of_Europe
Address Paseo de la Castellana 189/216 28020 Madrid, Spain
Coordinates 40°28'0.556" N -3°41'16.935" E