You can choose from those two possibilities to reach Galdós Residence:
a) Take a taxi to the following address: Ramiro de Maeztu, 2 (Residencia Galdós). It takes 45 minutes approximately and costs about 30-40€.
b) Take the metro line 8 (pink) from the airport to Nuevos Ministerios station. It takes about 45 minutes and you can pay with credit card or cash (1€ + 1€ supplement). Then take the metro line 6 (grey) to Metropolitano station (10min). From there, follow this map walking (400 m, 5 min aprox.):