Kitchens are rooms devoted to the preparation of food. Most homes, including castles, have kitchens.
Old English cycene, of West Germanic origin; related to Dutch keuken and German Küche, based on Latin coquere 'to cook' (Oxford Dictionary)
The Dursley's home had a fireplace in the kitchen. This feature suggests that their home was built before World War 2, before the advent of central heating.