Castell Coch (in Welsh, "Red Castle"), is a castle standing on the hillside above the village of Tongwynlais , north of Cardiff, Wales.

Very little remained of an original Norman castle by the mid-19th century, when John Patrick Crichton-Stuart, 3rd Marquess of Bute conceived a scheme to rebuild it as a medieval-style dwelling for his family. He employed the architect, William Burges , to design and build it, and the result, though it outwardly appears like a storybook medieval castle, is a complete fantasy. The interior decoration, in similar style to what Burges had already achieved at Cardiff Castle, is equally fantastic.

The castle proved too small and too difficult to access for the family to make great use of it, and was soon abandoned as an alternative residence. It is now in the care of Cadw and is a popular tourist attraction. It is also frequently used as a film and television location.