The entrance to the bay is lined by the Sardinero beaches, where the Isle of Mouro with its lighthouse can be found.

The municipalities within the administrative comarca are as follows, listed below with their areas and populations: Several rivers empty into the Bay of Santander.

Its materials are composed of clays and salts (specially Keuper's gypsums) that ascended taking advantage of the faults.

This movement generated an increase of the fracturing and an important dragging of rocks from the outer layers.

The weakness zone generated by the Keuper's clays made easier its erosion compared with other sandstone or limestone areas, which involved the advance of the sea and the formation of the bay.