Saint-Cast-le-Guildo (French pronunciation: [sɛ̃ ka lə ɡildo] ⓘ; Breton: Sant-Kast-ar-Gwildoù; Gallo: Saent-Cast-le-Giledo) is a commune in the Côtes-d'Armor department of Brittany in northwestern France.

It is port city on the English Channel as it also has a nautical center, the Centre Nautique de Saint-Cast (CNSC) ranked 3rd to 6th in the nation.

The English first attacked the region of Dinard by sea, but were stopped at the Rance by the Vauban fortifications.

They were forced to retreat to their fleet in front of St-Cast, where Emmanuel-Armand de Richelieu was waiting for them and launched an attack on the beach while the British were fleeing back onto their vessels.

[4] Saint-Cast features many of the typical dishes of Breton cuisine, such as the Kouign-amann, or the local specialty, Le Castin, which is originally what we call people from there, or in this case the cake.