Ruthin Castle (Welsh: Castell Rhuthun) is a medieval castle fortification in Wales, near the town of Ruthin in the Vale of Clwyd. It was constructed during the late 13th century by Dafydd ap Gruffydd, the brother of Prince Llywelyn ap Gruffudd, on a red sandstone ridge overlooking the valley. Part of the ancient walls still remain and now form part of the Ruthin Castle Hotel.