The Torre de Don Borja is a 14th-century defensive tower that now serves as the main tourist information point and a small exhibition space for the town. It stands at the entrance to the historic centre and gives a good sense of the fortified character that Santillana del Mar had in the medieval period, when noble families competed for power and land along the Cantabrian coast. The tower's name comes from a local noble family rather than any connection to the infamous Italian Borgias.
The ground floor houses temporary exhibitions on local history and the region's cultural heritage. The square outside the tower, Plaça Mayor, is the central gathering point for the village and a pleasant place to sit after visiting the Colegiata. Several of the old noble palaces around the square still bear their original coats of arms, worn by wind and rain to different degrees.