There are a lot of buses that connect Madrid, Bilbao, Hendaya/Irun, with Santander. The bus company that connects Hendaya-Bilbao-Santander, Madrid-Santander and Barcelona-Santander is ALSA ( phone: (+34) 902 42 22 42). 

The Madrid-Santander route is made also by Continental-Auto ( phone: Madrid (+34) 91 5330400, Santander (+34) 942 225318). 

All buses arrive at Santander bus station, which is in front of the train station. Once you arrive in the city it is possible to use the local buses, that have a stop 100 meters away from ACORDE, or use the local taxi service (phone: (+34) 942 33 33 33).