Castricum is a municipality and a town in the province of North Holland in the Netherlands. Castricum is a seaside town in the province of Nort…Castricum is a municipality and a town in the province of North Holland in the Netherlands. Castricum is a seaside town in the province of North Holland. It attracts tourists who come mainly to visit the beach and nearby dune landscape. Lake of Alkmaar-Uitgeest is in the vicinity, with facilities for sailing and windsurfing.