Madrid has high quality space available in the business center, where ‘prime’ rents exceed by more than 20% those of Barcelona.
Overall, it is estimated that in Madrid there are 1.5 million square meters available, of which 220,000 would be free in the center of the capital. Among the available spaces, the following offices outstand: Torre Foster, Torre Europa, Castellana 81, Castellana 77, Castellana 200 or Plaza de la Independencia, which are, mostly, refurbished grade A products.
Source: http://www.expansion.com/empresas/inmobiliario/2017/10/06/59d76f9822601dcd558b45aa.html